The weapons/vehicles used in halo 1 were the EXACT weapons/vehicles from the Reach battle, every pelican, every warthog, every assault rifle, and every havoc tactical nuke was loaded onto the ship from Reach probably not even a day before the Covenant invade. what I mean is there would be no opportunity for new weapon development or even a switch to different weapons that were already developed. I think however a silencer on the SMG and the pistol and a clip or two of armor piercing rounds (like in ODST) couldn't hurt... well it could hurt the Covenant pretty bad but you know what I mean.
EDIT:
Posted by: NinjaJamie29
Yes but the lazer and Battle Rifle were highly experimental at the time, so they may be in the game or may not.
The Spartan IIs were highly experimental at the time, but they were there weren't they?
P.S. I don't mean that the weapons/vehicles introduced in halo 2 or 3 should not be there, simply that older versions of the weapons not only should not but would not exist.
[Edited on 10.02.2009 11:18 AM PDT]