Maybe not to you. To them, big difference. It's not possible to block delivery to non-subscribers on the radio, or I'm sure they'd try it. (This is already happening somewhat with TV, as there are far fewer and in many cases zero games on over-the-air stations in local markets.) If you look at the history of MLB Advanced Media you will find that nobody has been better at maximizing online revenue, except I guess Apple. MLB has had its servers in everything -- don't know if this is still the case but for many years they were the technological know-how behind streaming the NCAA tournament online. It's a new technology and the customs are being made as we go, and MLB was very wise to create a pay model for its product.
Put it this way: If MLB had been in charge of newspapers 12 years ago, I would wager that newspapers would be an enormously profitable asset.
The price point is not obscene. If it's this big of a deal to you, $20 for the year is a pretty good bargain.