Everyone has the right to treat his/her OWN property rights with disdain or indifference.
No-one has the right to treat others' in that way.
YOU may consider the giving of credit sufficient for YOUR peace of mind, but others definitely do not.
This is not about 'paranoia', it is about preventing the erosion of your property rights.
mschleisner ... the difference between Wincustomize.com and Topdownloads.net is that with the former the OWNER of the artwork is submitting it themselves for display/distribution and the act of so-doing indicates consent for its distribution. With the latter a person or persons unknown has TAKEN your artwork and has reposted it on a site outside of your control and consent. You should NOT now be forced to jump through hoops to have the work removed....it should NEVER have been posted there in the first place.
Here's a quite valid hypothetical.
You upload your works for public [free] download. You become rich and famous and realise you want to now charge for your works. You subsequently delete/remove them from all the sites you uploaded them to....and instead post them for sale elsewhere. No-one buys them. You then discover they are being distributed elsewhere freely....on a site you were unaware of.
This is why you CANNOT be lackadaisical with your property and its protection.
Whatever commercial success sites such as topdownloads.net may be enjoying is purely because of content they have no legal permission to be distributing.
At no time did I [or clearly very many others] consent to the commercial profiteering of our works by an unknown third party.
In contrast, we ALL did just that with our submissions to Wincustomize.com, and Deviantart.com, and all the other LEGITIMATE public art/skinning sites.
If an artist openly goes on record [through inaction] of failing to protect his own copyright it can come back to bite him in any future litigation against similar issues....