The money Trolltech receives goes into improving Qt, which is Free and Open Source software and which directly helps FOSS developers and users like myself.
The fact that unscrupulous makers of binary blobs need to pay a tax that goes into improving FOSS software is a very positive thing. This is how copyleft was intended to work from the very beginning, see the essay by RMS titled
Selling Free Software.
Trolltech has been very responsive to ensuring compatibility with other FOSS licenses, evident by the fact that they have
dual-licensed Qt on all platforms under GPLv2 and GPLv3.