Quoting the original AD&D Dungeon Master's Guide, regarding the use of miniatures in the game:
"Figure bases are necessarily broad in order to assure that the figure will stand... Because of this, it is usually necessary to use a ground scale twice that of the actual scale... squares of about one actual inch per side are suggested. Each ground scale inch can then be used to equal 3 1/2 linear feet, so a 10' wide scale corridor is three actual inches in width and shown as 3 separate squares. This allows depiction of the typical array of three figures abreast, and also enables easy handling of such figures when they are moved."
In short, the corridors were drawn ten feet wide, but with the assumption that ten feet was enough for three people fighting side by side (three squares), not two. Since 4th ed divorces squares from actual distance measurements anyway, I'd say you're perfectly justified in following the Great Gary's advice and upping your maneuver room by half.
Other than that I'll just follow stripes's lead and say combine lots of rooms into one encounter. Don't have the orcs (or whatever) sit back and wait for the PCs to clear out one group at a time, have them rush toward the sound of battle, fall back for reinforcements, and in general make fights bigger than they first appear.
