If Surface RT is to be offered to consumers at $199 then presumably Microsoft have some way of making the money back?
The app store argument doesn't work; they only take a 30% cut. If they lose $50 per unit they would need to sell ~$150 worth of apps to that user to break even. If they lose $100 per unit they'd need to sell ~$300 worth of apps to that user. Not going to happen.
That leaves a subscription model. It's entirely plausible that they could offer the Surface on this basis. If it costs them $300 to manufacture each Surface unit, and another $50 to get it to market (distribution, support, retailer profit) then they're taking a $150 hit on each unit. To turn that in to a decent profit, they could offer it on a $10/month sub for two years; $90 per unit profit, plus app store revenue. They could also combine this with another service. Xbox Music is the best example here. A $20/month sub might work here, and they might decide it looks better value for money than the Surface alone.
As far as I can see, there's no reason why the same subscription model couldn't be offered to Asus, Dell, Lenovo and Samsung for their RT tablets. It would be a sensible move on Microsoft's part, negating the accusations of unfair play (from those OEMs). If this is the case, it would explain why Acer are so annoyed. RT is going to hurt their business.