Very true Yves, but certificates are a nice little touch that would not require much work. It would not distract the hard-working techs very long I imagine, its just an automated PDF mailed to your email address, that you choose to opt into only if you want to. Folding@home, run by Stanford U., certainly saw merit in the idea.
And paper certificates can:
1. serve as a discussion starter in your office or study wall
2. Paper certificates live on long after your account has closed, due illness, death or some other reason, and if held long enough, they then become historical documents. People could start to collect them just like people collect stamps, autographs, and old stock certificates.
3. Seeing them may even get family or friends interested or motivated, and that can only benefit WCG, whose membership has been fairly static over recent years.
4. If made available online, it wouldn't even cost WCG for paper an ink, only those interested would download and print them.