You know, that is true, but this kind of answer is my pet peeve. This is what drove me crazy in the Linux community: I would say that something isn't working right and they'd say "It's open source, fix it yourself." Yeah, that's great and all, but I'm not a programmer (well, I know php and C#, but just as a hobby). This is why non-tech people don't use Linux.
To be fair, the tech support for consumers for something like Windows or Microsoft Office is also non-existent. Only if you're part of a large enterprise and can apply pressure through account managers you have any hope of getting your issue solved in any realistic time-frame. So usually with Windows, if something fails, you just live with it or work around it (using some workaround that you found on the net).
For Bitcoin Core (and most open-source software) it's on an best-effort basis. If it's a serious problem that is possible to reproduce (or you make very detailed bug report) it usually gets resolved quickly. If it is just a minor annoyance, or something that can be worked around, this can take much longer - if it is no-one's pet project.
If something really bugs you, you could hire an consultant/programmer to fix it for you (or through the vendor with a "service contract"). This applies to both open source and closed source software.
In a community project you *may* find someone crazy enough to do it for you for free as a pet project (for example for the 'cred'), but do not take this for granted.
In this case, Qt is themeable and themes exist 'out there'. Either you can find a theme and have someone integrate it into Bitcoin-Qt (may not even require c++ programming). Or have someone design a theme for you from scratch (probably going to be expensive - like developers, designers won't work for free unless it's their pet project, and designing Qt themes is a rare speciality).