But the OP has an AMD chipset, and thus he can only use Microsoft AHCI driver or the ATi/AMD chipset driver. Of those two, only the Microsoft driver passes along TRIM.
If you're on Intel platform instead then you're right of course. The Intel passes along TRIM in AHCI/IDE and RAID mode to SSDs just fine, as long as they are not in a RAID themselves. Essentially RAID mode is just an extension of AHCI, but it cannot be handled by the Microsoft drivers, and thus, until Intel modified their drivers to include TRIM in AHCI mode, there was no way to get TRIM support on the Intel controller running in RAID mode; but even in AHCI mode many people did not receive TRIM because they installed chipset drivers including the Intel driver which replaced the Microsoft driver.
Now at least these problems are gone on Intel platform with new 9.6+ drivers, but on other platforms like VIA, AMD, nVidia and add-on cards like Silicon Image (including SSDs like RevoDrive) you would have the same problem: the proprietary drivers don't support TRIM, and thus the Microsoft AHCI/IDE driver should be used instead to avoid degraded performance due to lack of TRIM.
On Linux/BSD the "RAID" hardware just registers as SATA controller, and thus TRIM works on all normal SATA controllers, FakeRAID or not. So it's purely a software limitation of the vendor-specific Windows I/O drivers. Kind of a shame reputable companies like AMD don't have TRIM support by now; they do have 6Gbps but no TRIM in their drivers. Many people may not realise this and run with AMD driver instead of Microsoft driver. All these issues with TRIM are rather messy, IMO!