Great blog - loving the RF bonanza at the moment. From 10 kW of VHF to a few milliwatts of UHF in the space of a week - I'd send my WWII vintage HF Wireless Sets Number 19 for a mailbag teardown candidate, if the postage to Oz wouldn't bankrupt me...
Wireless microphones cause some headaches for spectrum regulators and designers. They have to be analogue - you can't have any delay for live music shows - and they have to have lots of channels, plus you can't accept any level of interference from other services and size/power issues means they really have to be in bands where lots of other things already live (usually in the middle of the TV UHF band, where the other things can be really quite brutish). Particularly problematic for those who try and do white space RF, which tries to slot itself into unused parts of bands allocated to other services. Small, susceptible, hard to detect and very, very mobile.
The interference rejection is one reason why there's so much filtering and good solid RF engineering in those things. I'd love to see a circuit or some RF performance specs for them.