But what you are really paying all that extra money for is for those extra 10% of features that you might be able to find a workaround for 1/2 of them.
That is where the money is going.
True, it all depends on what your demands are. But I suspect I can live with Pixelmator's current (2.0) toolset. After all, I got a lot of "real work" done in Photoshop going all the way back to version 3...not CS3, 3.0, in the mid-1990s.
The other thing is that, like the Photoshop and CS software, Adobe itself has become slow and bloated as a company. They're entrenched and, as is common with such companies, tend to spend an increasing amount of their resources protecting what they have instead of innovating (not that they don't at all, content-aware fill for example is awesome). They can take forever to come out with new features that users are actually asking for, or to fix long-standing niggles. Do you remember how long it took them just to put decent typography support into PS (kerning, editable type layers, etc.)? It took until PS 5.5 for that.
Pixelmator is a young, hungry company. That allows them to move much faster and try new things. It's much easier to get in direct contact with a Pixelmator dev (like through their blog), than it is to get ahold of a Photoshop dev, and that dev would likely have a much better chance of being able to have direct and immediate influence on the product based on your feedback. Pixelmator may still be lacking, but it's not complete. I have a lot more confidence in Pixelmator rapidly advancing than I do Photoshop. Furthermore, it's a Mac-only program, meaning no weird interface compromises (Pixelmator can use new Apple UI elements, Adobe is stuck with their aging cross-platform widgets) or waiting for OS changes, like CS adding 64-bit support or moving away from deprecated Carbon APIs.