This has been the subject of many heated discussions in the embedded world. For a start, see http://www.embeddedrelated.com/usenet/embedded/show/91196-1.... and http://www.microchip.com/forums/tm.aspx?m=292995 for a start.

There are code size limitations (your binary must be no larger than 16 kB, some of these devices have 128 kB of Flash), there are optimization restrictions (you can't use -O3 or -Os, and some -f flags are disabled), and the libc is closed-source. These are the things that bug most people.

The OP here is pointing out issues with closed-source peripheral stacks. That's a whole different issue.