If it's worth its money, it will scale down too.
EDIT: To be more precise, the ability to scale down is removed from AAA titles (or strongly limited) as they don't have time to deal with and test for the huge amount of hardware combinations. An inherent problem of existing engine design. I would definitely not put money down for something which works only well on one hardware configuration (how I hate looking up my processor name in the "supported" tables <.=.< ... it's never going to match for more than one game). [ fuck this 1min edit limit ]
Beating TA-S graphics with 10 tanks is one thing (I never tried playing TA-S in anything other than the default top-down camera), keeping the same advantage when 400 unit fight-it-out is something radically different.
Hopefully Unigine won't be forced to choose the easy way out. (By setting a low unit count limit ala Starcraft)