True for AOL as an internet service provider, but you can get an AOL email account for free without having AOL as your ISP.
Name another ISP - any major ISP that provides/supports IMAP account access. I'm not aware of any.
ATT/bellsouth offer insentives so that their customers bundle their phone and internet services.
True, but this has nothing to do with Apple and the iPhone. AT&T sells a significant number of carrier locked phones, with the iPhone being only one of them. Apple has nothing to do with AT&T's bundles services for phone and internet services, and the same for the type of email account that AT&T/BellSouth provides/supports as an internet service provider.
You can get a free Gmail account, which can be accessed as an IMAP account with an email client on your computer and with the iPhone's mail client. There is no rule or law that requires you to use the email account provided by your internet service provider. I haven't used the email account provided by my ISP for the last 5 years or so, which can be accessed as a POP account only.