I don't see the two products as the same market. What casual fan is going to get a 2600+?
Hell, like everyone here, I grew up with Atari, but I don't have my childhood 2600 or its games anymore. I'm not going to get a 2600+ and track down old cartridges.
The My Arcade seems like a decent option for casual fans as is, but with potential to add games. That's much more interesting to me at least.