I don't use reddit, so I don't know if it's worth comparing to bitcointalk or not. For the best post quality, bitcointalk may still be at the top for online bitcoin forum compared to other forum. But in my opinion between Reddit and bitcointalk have a different rating system. A Reddit user doesn't need HQ quality post to earn karma, because fame and number of followers will have an impact on the amount of karma you get. I think the same post rating system applies in bitcointalk and that is a merit. There's an emphasis on post quality as a condition for getting merit, I think it's different on Reddit. If my assumption is wrong, please correct me.
Nah, its a pretty bad idea to compare Reddit's upvotes to Merit here on the forum. Reddit's system is fundamentally broken, and is very easy to abuse. Basically, if someone wanted to they could control what is seen by others on the subreddit by creating hundreds of accounts, and down voting whatever they want. Merit here on the forum is only given to those that have earned merit or have been selected by theymos for their merit distribution, and eye for spotting posts that align to his goal on Bitcointalk, which is usually the higher quality posts.
Upvoting isn't judging the posts quality, at least that's not its intended use. Its used to help upvote content that they think is relevant, and users should see, and down vote things that they shouldn't see. That's basically it, its not really tied to the quality of the post, at least not primarily, and is only loosely associated with it. However, its most definitely misused by many of the users over there.