"It only takes a little extra work to make your PC games play on the PC, and make gamers happy"
Sadly, that's naive. Like any other software company, there are diminishing returns for features / revenue. When the product is slated for release on Xbox, PS3, and PC it is typically done with one codebase with platform specific code where necessary. You often end up with a common denominator where the PC people usually feel left out in the cold.I can attest that it takes a monumental amount of work to support the myriad graphics card configurations for the sole purpose of getting your game to look/feel ROUGHLY the same on all three platforms. To customize the game for one platform would be at the expense of the other two (from a development, production, and QA perspective) and it often doesn't make sense to those paying the bills.
Sometimes the PC gets a dedicated port (such as Mass Effect for the PC), and those things that make PC gamers smile get added. However, this port is essentially a new project (SKU in retail games parlance) that is greenlit only if the console versions of the game have sold well enough to warrant it, and is typically done by a third party under extreme time pressure.
All these factors contribute to less polish, which everyone involved is keenly aware of. Hopefully I've illustrated that this is a complex problem that can hardly be addressed by a "it doesn't take that much more effort to do a good job" platitude.