Coinbase delays the disbursement to keep you from chargebacking. Same thing happens in Dwolla. If you send a money order over snail mail to an exchange, you can get your funds available same day (they receive it).

It isn't anything bitcoin can change - it is moving money from a chargeback system to one without a way to reverse transactions. If they allowed chargebacking, they would be exploited and go bankrupt.

You don't have to buy bitcoins with coinbase. They use coinbase to accept them, but the donator can get them from any method they choose, including coinbase, campbx.com, localbitcoins.com, friends, mining, etc.

But none of those methods can happen on the checkout page. My mom already knows her credit card number; why is she going to put off her purchase until she can buy BitCoin somewhere else?

The easiest way is to purchase bitcoin from a friend or coworker. Hand them cash, and they should be happy to show you how to download a wallet app, and send you some bitcoin.

Transactions in person and Bitcoin ATM's will be the bread-and-butter of exchanging fiat money for BTC as it gains widespread adaptation.