Using get instead of post for these kind of actions is just asking for trouble.
If HTML had a method="post" option on <a>'s then it would be no problem to always use the proper HTTP verb, but we have to satisfice with what we've got.
That said, if you're already using javascript (as news.YC is), I really don't see why you wouldn't make use of xhr. In which case you could submit the request as a post.
Note: I haven't poked around enough to see if news.YC works without javascript. If they degrade gracefully, more power to them, and I can almost understand the decision to do it the way they have.
Edit: Or so I thought. I'm wrong.
It turns out there's no standard for this, so who knows what you can do today. But practically, Google Web Accelerator doesn't prefetch links with a query string, at least currently. So Paul's voting links are A-OK with GWA. And that's the only one that you need to worry about, at least today.
http://webaccelerator.google.com/webmasterhelp.html#prefetch...
I've edited my post. Thanks for your reply.