While at this point I haven't studied the situation enough in order to confirm or deny any actual violations, let me state this: The number of GPL Violation reports/allegations that we receive at gpl-violations.org on HTC by far outnumber the reports that we have ever received about any other case or company.
In addition, HTC seems to have had a long trail of problems with GPL compliance in their devices. Ever since they have started to ship Android devices containing the Linux kernel, licensed under GPLv2+, we have received those reports.
The reason I have never taken any legal action is merely a result of the fact that HTC seems to first introduce their new devices in the US, then at some point release the corresponding source code before shipping those devices into Europe and Germany. So by the time the devices are sold over here, the legal issues appear to have been resolved before.
Nonetheless, I think it is outrageous for a company of this size and significance in the market to consistently commit copyright violation (or at least walk borderline with it) and thus mistreat the very copyright holders that have created the operating system kernel they use in their devices. The linux kernel developers and the Free Software community as a whole deserve fair treatment.
Also, the competitors of HTC deserve fair treatment: Samsung, e.g. is very forthcoming with their Android phone source code releases. If I was them and would see HTC to fail to comply with the GPL, I would consider filing a unfair competition lawsuit...