I assume Sprint is offering the Evo for $199 because they want to be price competitive with the iPhone. Don't forget you also have to pay the $10 additional per month ($240 over the life of the contract for functionality only a handful of users will actually benefit from in 4G areas) so they are probably willing to subsidize the price of the phone more than usual. And that doesn't even count the people that will buy into the $30 hotspot add-on.
It's more like the Verizon sales model, the way Verizon sold the TP2 for $199 out of the gate but the monthly plans were more expensive so you'd pay for it on the back end. Besides, being at that sub-$200 price point is right about at the impulse-buy cutoff for a lot of gadget freaks like us.
I think the Evo will fly off the shelves and I hope that it is successful. But not so successful that they don't build a keyboard version someday. And a good keyboard, like the TP2. Let's hope HTC realizes they struck gold on that one after many years.
I bought my TP2 from Ebay for around $300, and I'm absolutely thrilled with it. So much so that I walked brazenly into an AT&T store last week and bought a set of screen protectors for the "um, Tilt 2...for a friend". So I'll be keeping it for at least 3 months, which is like forever to me.