We are taking great care in terms of performance and memory.
One thing that pains me is when people talk about BF3 as if Elemental is somehow dealing with something easier. BF3 maxes out at 64 units in a game world that has a handful of buildings (I love BF3 mind you, I'm just saying that it's not pushing your hardware as much as you may think in the ways you're thinking). Elemental is dealing with hundreds, often thousands of units where each one is different (i.e different boots, helmets, gloves, etc.) along with many different buildings.
The art style is designed to limit the impact of that (i.e. our units and buildings are a lot less detailed) but it's still nothing to shrug off.
The challenge is always one of finding that sweet spot in terms of performance vs. graphics vs. interactivity.
With WOM, our hands were very tied on what we could do because every solution always involved using more memory which we were in short supply. Pixel Shader 3 lets us do things more easily.
Right now, for instance, we don't even have a graphics quality setting. The goal with the beta (beta 1 series anyway) is to optimize performance as much as we can with the graphics maxed and then introduce other options to lower the graphics settings.
Right now, if the game is running well for you that's outstanding. But if it's running slowly, it's not surprising and nothing to sweat because it shouldn't be running that fast for most people. It should, ideally, be running too slow for approximately 50% of the user base.
It's a LOT easier to trim back on the polygons and texture sizes than it is to try to increase them later.
FE and WOM are two very different beasts. I don't mean from a "quality" argument either, I mean architecturally, they don't share similar issues. They have their own unique ones. 
