The app store has a few benefits. The biggest one, for paid software is that if I format my computer or move to a new computer my license come over with my Apple account. I don't need to worry about remembering an account and license keys for each each.

I can't count how many apps I've paid for but I don't have installed right now because I lost a hard drive and my license keys with it.

Though I'm guessing with monthly billing it is more a username / password thing for you vs a key. (I haven't tried it yet, sorry).

The second benefit is not having to give my billing info to yet another company.

I'm not unlikely to install an app not from the app store. But I'd say I'm... complete guess here... 30% more likely to install it if it is in the app store.

And I can also say that if I have the choice between the two (same software on the app store and off), I will always do the one in the app store because of the previously listed benefits.