[Briareos]

I see alot of people advocating "hardsuit" technoclogy. However this carries with it two flaws of bipedal technology. First, small robots are generally refined versions of large robots. Take a look at computers, the old ones were very large, and the new ones are very small and much more powerful.

Because the speed of light is finite and thus the smaller distance it has to travel the shorter the time for a signal to be transmitted. Let's just not go into the fact the really big ones were mechanical and involved sautering the connections manually, while the present method is multilayer photomachining and the plants to be able to build such things cost BILLIONS, with a B. Yes, with advancement in manufacturing technology you can have tighter tolerances in manufacturing.

The second primary flaw is a power system. Large units(we're talking a human-lacking machine over 15 feet) have more space for the effective equipment and power systems.

Translation: surface area goes up with the square of the scaling factor, volume by the cube.

Overall since most combat does not end with hand-to-hand a "battle suit" in a BGC sense would be pointless.

Translation: Kevlar sucks at stopping edged weapons, so the apparent reason to use plate armor would be to stop edged weapons.

In your average combat, you need ranged weapons. Since most advanced ranged weapons are heavy the simplest solution would be "movement enhancers". Which would be more along the lines of the Batman Beyond battle suit. Servos, motors, ect, are placed on the joints to facilitate faster movement and larger weight loads. Also due to their size and area coverage they would require less power than a full-body suit. However, as with all technology, it would start with something bulky and ineffective, and progress to something sleeker.

Translation: Thus PAFs (Briareos's term) have been developed starting with the clumsy hydraulic Hardyman:
and proceeding on to refined versions like:
This Japanese suit for medical purposes, and the Darpa concept, which I've lost the good picture of.

Also, because this design lacks the need for balancerrs and legs, it can be applied on a humanoid level. If you were to build machines like the T-1, 2, 3 ect..(if you've seen Terminator 3 you know the knd of robots I mean). They are small, pretty maneuverable and well armed, however being small you run into the problem with stairs again.

Nevermind the existing Talon series of robots, which can climb stairs mount a wide variety of weapon systems, and avoid the inefficiencies of wasting time with a humanoid top. Not to mention are man portable, and unlike the iRobots, favored by the troops in Iraq. To bad, Foster-Miller doesn't have the same kind of marketing division as the manufacturers of the iRobot.

EDIT:
For those looking for the MOAG treatment I bring you to a treat from the annels of WW2 history, presenting:
The Dora and the German land battleships from achtung Panzer and Answers.com. (Note: for those who aren't paying good attention the P-1500 would have mounted a Dora cannon.)

EDIT2:
Additional linkage:
A nice site on the Abrams and Merkava Mk4. Note the fate of the car that got in the way of an Abrams needing to move there, plus the fireballs when the main gun fires in the other pictures. I hope you enjoy it.

EDIT3:
If I'm understanding you correctly General in your reply, you're basically setting up a scenario where you have to use mules to transport things in (thus constraing road size severly, and any wehicle that can go through it), attacking a fortified position that can take fire from towed howitzers, is for some reason protected against airpower, and I'm not sure whether you actually understand what a recoilless rifle is. Considering a man carriable 83mm HEDP rocket can do 8" concrete, 1' brick, or 7' wood reinforced sandbags that pretty much means the thing is a fixed fortification. Carl Gustavs or SLMAWs, which are just the man carriable recoiless guns, not the mention the AT-4 which has replaced the M-72 is an 84mm tube. In which case there's a big question of why we can't just drop a bomb on the thing.

So how pray tell is your gigantic mech with this superpowered arty piece, that can't fit on the road, and can't be dropped in because you waved airpower going to get in there? It's not a small organic lifeform, and thus the various narrow routes us small guys can take advantage in rough terrain that larger vehicles cannot don't even come into play. If you think it's going to climb the cliff, I want a reasonable mass number, and even then I can pretty much say flat out the rock is just not going to hold even if the hand and footholds are there. The difference between the stress from holding ~60kg and 2000kg (2 metric tons) on roughly the same area is not exactly comparable. Nevermind it's kind of a sitting duck for a long time, while attempting to pull off such a thing. I recognize you're trying to put your theoretical mecha in the role Heinz Guderian recognized as being revolutionally with the tank, but you need to actually show why it could go where you claim instead of just asserting it can, especially after the claim has been challenged. Additionally, no you shouldn't just go and classify everything even theoretically tangentially related mecha. A air-pistol is not the even remotely the same in design requirements, specifications, and potential uses as a Battleship gun.