I think it more likely that our testing is limited rather than Blizzard's randomisation being flawed by a large amount.
Here's some interesting mathematics:
If I flip a coin ten times, what's the chance that it will come up heads exactly five times?
It's 63/256 or 24.61%, just less than 1/4.
If I flip a coin a hundred times, what's the chance that it will come up heads between 49 and 51 times?
It's 23.56%, just less than 1/4 again.
If I flip a coin a hundred times, what's the chance that it will come up heads between 45 and 55 times?
It's 72.87%. That still means that in the long run, over a quarter of all the results will be either significantly lower or higher than 50 'heads' outcomes.
In any case, it doesn't seem like anyone has done enough testing to conclude that blizzard's probability of outputting a 'set' result is necessarily greater or less than the ideal 50% in the long run average anyway.
If you don't want a great fluctuation in results, probably the simplest thing to do would be to make the results only have a limited range, say from 40 to 60 instead of from 0 to 100, by starting at 40 instead of at 0, and having less randomisations.
Tux's method is cool, but maybe unnecessarily complex for an effect that few people will notice.