"Sort of interchangable" would seem a more accurate way of putting it.
As I understand things, TRIM requires a SATA interface. So it would depend on the interface between the drive itself and the enclosure's chip and the chip in the computer itself. If the enclosure is USB, then no TRIM. Which is also the case with many current drives that have both USB and Thunderbolt sockets, but the enclosure/drive electronics are USB with the Thunderbolt socket basically being bolted on to that.
Some people claim that TRIM over USB might be achievable, so long as the "right" USB chips in the computer and drive are used and the driver and operating system also support TRIM in the way required to make it work over USB. Neither Windows nor OS X support this however, nor does there seem any way to find a chipset confoguration that would work or suitable drivers. In other words, as far as I'm aware TRIM over USB may be hypothetically possible but for real world purposes isn't. A situation kind of like audio interfaces and firewire on Windows, only even more complicated.
And some claim the TRIM command is superflous and the drive's own garbage collection plus the OS file system will do a good enough job without it. Though those claims are often found in articles concerning Yosemite and older OS X and using USB or other SSD drives (there were configuration issues with implementing TRIM on any non-Apple drive which I won't bore you with, and the issue is no more anyway). OS X and it's file system aren't Windows so even if the ”no TRIM required" claims are true for OS X that may not apply to Windows.
In any case, if TRIM isn't required, or at least very useful, why do MS and Apple bother implementing it at all?