At least on this web site they need to work to have an old account, so your comment won't be at -10 quickly.

Edit: Here is a business idea to get round the voting problem by paying money from China, Russia, Microsoft (they stopped after the court cases?) and other astroturfers. A browser plugin you install where you configure the bank account and web sites you have accounts on. The plugin votes for you and a bit of money is put into your bank account. You could instead work on detectors and honey pot comments (to detect these users), before HN et al are destroyed.

Edit 2: It should be possible to hide the voting plugins better by voting up comments on sham accounts, which then are used for down voting. I see a whole new application for data mining to detect this. :-(