^^ maybe, but then you have the other side of the coin. By doing it monthly instead of yearly and being automatic people are less prone to cancel their subscription (or let it lapse), even if the price goes up. There will also be a certain percentage that will be 'out of sight, out of mind' where the subscription will continue to be renewed.
The less they can get their customers considering whether they're renew or cancel, the better off for Adobe it will be.
So, while they might win some extra over such as yourself, the question is would they lose more in lapses of renewals and cancellations than they would gain?
In addition to this, I think one of the main benefits of the subscription system (for Adobe) is all about the bottom line. They can budget and forecast much easier this way without being worried how many people will be interested in the new features they release with their new version.