When Pivotal first launched they had a free version for a while before started to switching pricing. Now, I understand there is a big no-no about raising the price later. However, I think there is a world where they can offer:
A - personal free accounts. Or free account for team of < 2.
B - announce the price but provide a 6-9 mont grace period just so they can get a nice momentum.
Now, they might be charging from the get go for fundraising reasons. Basically so they can go to investors and say: look we got X number of real paying customers in Y months. Which makes a real good case for getting investors.
That said, I love the UI. But I wont invest anytime on it yet, unless I know I can use it for free for a few months, or if there is strong social value that proves it can really help projects and requirement gathering process.