Just to throw in my 2c as an iOS developer... their bluetooth API is closely limited in features (keyboards, audio out/in, call control, music control, communication with other iPhones and 3G tethering). I think it's jumping to conclusions to say they don't want to support other features, more likely they just can't be bothered as the bluetooth specification is a complete disaster. Chances are they will implement more of the spec one day.
SPP is likely to be pretty high on the list of things they might add, since they already do something similar over USB. Though I'd put my money on developing a more modern protocol, instead of choosing an existing standard based on a protocol developed in 1962.
For larger companies like DeLorme I bet Apple would be willing to work closely with them. The thing can track your footsteps if you wear specific Nike shoes...
That's a lot less useful than satellite communication.
You can do anything you want communicating with custom hardware over USB, using the dock connector. Plain old simple arbitrary data transfer between your software running on the phone, and whatever hardware you build. Your hardware can even instruct a specific app to launch whenever you plug it in. So it's entirely possible for Delorme or anyone else to do whatever they want via that route.
For example TomTom has a car kit with it's own GPS receiver that's too bulky/power hungry to build into a phone, as well as a bigger speaker to improve turn-by-turn directions, phone calls, etc.
If I knew a bit more about hardware, i'd love to create a mount which charges my phone and hooks into the bike's ECU to record diagnostic info into a gpx file, which could be used to overlay speed/rpm/throttle position/temperature/etc onto a helmet cam video...