Leaving comments along the lines of "I tried it and it sucked because it doesn't support the US" is not, in my opinion, in line with the hacker news civility guidelines -- it's not constructive, especially when "all over Europe" is explicitly mentioned in the post's title. As for site portraying rent prices as "high"... it's all relative; those prices may be high for people in Europe, even though they might be paltry compared to SFBA.
What I didn't like was that it assumed that 5% higher than average was like some crazy high percentage and I'm getting totally fleeced and "Ooh snap! We warned you! You totally shouldn't have clicked this link! (except we baited you into it)"
It's the attitude the website presented, not the actual data. And it's constructive in so much as I don't want people to use this site as a guideline on how to communicate with its audience when they make their own websites.
5% of my rent is roughly $50 a month, btw. Not insignificant, but not enough to warrant its tone either. And I don't live in the Bay Area, thanks for making another assumption about me.
But I interpret their comment as more directed toward HN users than the creator of this site. That they felt cheated, seeing this link on the HN front page only to discover that it's lame and rude. I think it's perfectly fine to express that discontent in the comments, especially since HN doesn't allow downvoting stories.