That's pretty terrible excuse making, to be perfectly honest.
There are plenty of games out there that simulate TONS of things going on without the massive hit on framerate that SSE creates. Take Arma II for example - in that game you have planes, helicopters, ground vehicles, infantry, etc. running around real-time in missions (with dozens and dozens of active AI) with explosions going off, tracers everywhere, etc., yet you can still retain a great framerate. And the graphics in Arma II are first rate as well.
Another example would be Silent Hunter 5. Arguably a more believable ocean simulation, and on top of that it simulates naval warfare at the same time.
I have a Core i7 950 overclocked to 4ghz, a Radeon 5850 HD video card, 6gbs of DDR3 1600 memory, all on a streamlined and optimized Windows 7 install, and I'm barely able to exceed 30fps in some parts of the game. It's playable, but given how basic the graphics are.... it's unbelievably bad framerate. And that's without antialiasing turned on, which these days is a must have - when I turn that on I hit down as low as 10fps. Insane!
Before I built this PC a week ago I had a Core 2 Duo E6750 overclocked to 3.6ghz (and still had the 5850 video card). It was far from top of the line but also still above what the average user for SSE probably runs, and SSE absolutely crippled that system. 10-15fps on any of the port environments.
Given that this game has a niche audience to begin with, I can't see how it will be successful if you need a high end PC like mine to enjoy it without lowering graphics to very basic levels or playing it like a Powerpoint presentation...
/rant