Unless something has changed, you need a minimum level of reputation to upvote. If you are not a member of the site (I have a vague memory of starting with only 10 rep - I have no idea now) you have no mechanism to actually do as you suggest until after you've posted or asked a question that has gotten at least one vote.
I just created an account there after years of lurking and absorbing knowledge from other's questions and answers, but I only have 1 rep.
Oddly enough, I created the account specifically to upvote the answer that solved my problem of which another member had asked about, but I am unable to do so until I submit a problem of my own that has not already been answered.
Yeah, that's still true — people who haven't participated in the site cannot upvote. I'm not sure if there was a larger point that I'm missing. Things still get upvoted quite a bit even with the rep requirement (and you could make a reasonable argument that the rep requirement means the votes you get are marginally better indicators of quality).
