A quick correction: Most LAV's are assuredly not
similar to a tank
in armaments. They also, due to the need to float, cannot carry very significant armor
. As a result, LAVs (while useful for carrying troops ashore and providing light covering fire whilst doing so, or operating in swamps and other damp areas, or operating as 'heavy cover' for infantry-only engagements) are extremely vulnerable targets on a modern armor battlefield. Even if they are only facing infantry, man-portable weapons which are marginal against tanks (LAW
, etc.) are hell on wheels against this sort of cow, making its survival without massive cover dubious.
OTOH, in infantry-only light weapon battles (assault rifles, maybe a few SMGs) the LAV is a viable 'armored taxi.' As far as armaments, the American Marine Corps AAVP7A1 Amphibious Assault Vehicle carries only 1 cal-fifty machine gun and 1 Mk.19 40mm grenade launcher.
The LAV-25, the Marines' official LAV, tops out with a 25mm autocannon and coaxial 7.62mm MG - the former being the same weapon used on the Bradley M2 IFV. While this weapon can, technically, knock out tanks (it was reported to have penetrated the glacis armor of Soviet-built T-55s and perhaps T-62s during the Gulf War) it, too, would survive only moments against a determined opponent with modern anti-tank weaponry - even if only the man-portable variants. The troops know this, if only instinctively; at incoming fire, there is a strong desire to get out of the vehicle, rather than stay in - anything big and vehicular tends to naturally draw fire, and it's much much safer to be somewhere several yards away smooching soil.
A final note: ref. armies dumping MBTs for LAVs...this may be true; however, in these cases typically the resources aren't available to maintain the MBT and/or the proximate threat faced by that country no longer calls for them. MBTs are 'come as you are' weapons, and not having them at a critical junction can mean the difference between survival and annihilation. This is why the Taliban and various Afghan factions, despite having absolutely no infrastructure that worked and no resource base, still sank fuel, work and money into keeping a few of the Soviet leftover tanks operational. Whie they wouldn't be much use against, say, the U.S. Air Force, a force of fifty or several hundred foot soldiers approaching your village will definitely take note if what they had assumed to be a burned-out tank decides to start engines and turn towards them.