DNS supports TCP largely because of packet fragmentation issues with UDP. I don't have a lot of experience with it but from what I understand DNS attempts to switch to TCP (with varying degrees of success by implementation) when the size of the response exceeds or is expected to exceed the MTU.

DNS Supports TCP due to some responses to requests being > 64Kb

Initially for domain transfers, and now for DNSSec etc where you can get rather large certificates embedded.

Also it's rather handy if you're tunneling over a proxy that only supports TCP ;)

Yeah. For "regular" DNS (not zone transfers), TCP is mostly used as a fallback.