Let me clarify, my comment was in regards to personal exploration and nothing beyond that. Most add-ons have a basic, very limited, free option. The same goes for the pricing on Heroku's platform. If you're rockin' an app that needs to be production scale, baseline won't cut it on Heroku; frankly, you get what you pay for so I don't expect it to be free.
Point for point, GAE's baseline quotas are obviously better but it's not an apples to apples comparison in my opinion.
Google App Engine is another awesome PaaS which is really free, because the free quotas are huge compared to Heroku's tiny 5MB database.