I'm in the camp who thinks it is great to have it as a mini goal - I'm looking forward to seeing how much I can lose in those first 20 days and also, it's helping me stay on plan for that time. Supposedly, it takes 3 weeks to develop a new habit, so when I get my ticker, I should be in the habit of being on plan!!
It definitely isn't done to make anyone feel bad. The problem is, spammers would join, post all over the board, and then put a spam link in their signature boxes. Suddenly, that spam is ALL OVER the board, and nothing showed up in "New Posts" so that we'd even see it. So it takes us much longer to catch, and therefore to delete and ban.
It's a rare spammer that will join, make 20 posts that make sense, wait 20 days, and come back to spam us. This change has cut down the amounts of spam (and the work it makes for your volunteer moderator team) by a huge amount.