I would suspect there to be many reasons why they are not marketed for 700W, first reason that comes to mind is that far too many people actually believe that those specs mean something and would pass over buying them thinking they would need 700W to make the M80s work at their best, when in fact they work equally as well with much, much less.

From an engineering stand point most everyday items are spec'd at much less than what they have been engineered to with stand for liability reasons.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70