I disagree. If I started getting into the habit of throwing some bitcoins at gittip, I might be inclined to send a few over and keep them there with the intention of distributing them to people without having to do a new transaction each time. If they're just used as a way to fill my account there and then instantly changed to dollars, what's the difference between that and a bank transfer? (Except that there is no fee and no hassle.)
If you have subscribed with a credit card, and forgot about the subscription (but generally fine with it), the service would still receive weekly payments.
In case of bitcoin, if you have forgot (that would be the case for 80% of us), the payments are stopped.
But I completely agree that it's possible to implement subscriptions (read: automatic payments) on top of the existing Bitcoin infrastructure.
