Frequency too high for indoor reception
Clearwire operates on a 2.5 GHz licensed band. That's just too high for reliable indoor reception in many cases; e.g., it's far above the frequencies used by broadcast TV, even the highest UHF channel. No wonder those Low-E coatings on those windows block it.
It's gonna need an outdoor antenna for reilable reception. Fortunately the FCC OTARD rule will cover these antennas as well, and you'll be able to install one no matter what your Homeonwers' Assoication thinks of it. You're still SOL if you live in an apartment, though. That's only one of several reasons to get out of an apartment and into a real house, though.