As you can read in the 3GPP 127 007 8.5 the implementation of the at+csq
is optional (the command which suppose to give the signal strength). Apparently HTC hide this value from 3rd party applications and they probably have another way to achieve that value for display in their own proprietary Settings application.
The fact that other applications also cannot get that information justifies my case.
This issue is tightly related to yours - thay said that HTC is one of the OEMs that does not worth the modem related developing time.