The problem is that once you put the drives into a raid array, the OS and even most of the hardware in your system only see one drive, that is really an emulation layer on top of two drives. Trim commands can be produced, but the raid controller has no clue what to do with them. The SSD's only have data written to them, but in raid 0, the whole file may not be on one drive. The files get stripped across the drives so that several write operations can occur at once. Since that data isn't associated at a specific point on a drive there's no way to trim that space when the file is erased.
Some very smart people are working on this, its a thorn in the side of the SSD world right now. It'll probably take intel making a chipset that can recognize if an array contains a SSD, and a way for trim commands to be parsed correctly to operate in a sane manner.