I've heard of exactly one of the dozen-odd apps you listed, and that one only because it's been on the frontpage of HN so often. I don't have a copy of it though.
I think that people who customize their iPhones to this level just assume that it's normal to do so. Among people I know who have them, there's a sharp divide between the small percent who have seven pages of apps and most people I know who have maybe 3 or 4 apps installed.
The vast, vast majority of 'regular' iPhone users have never, and will never hear of the apps described in this post. For them, the default apps are just fine.
That's not to disparage the choice, just to recognise that regular users don't care about this kind of thing one bit.
The thing is, not everyone will customize all apps, but everyone will customize at least one app, be it a better todo list, a better IM, a better picture-taking app, or a better recipe database. Which is why the appstore is so popular.
EDIT: clearly the "regular users" I know are different from everybody else. The North of England must be a hive of phone-geeks living in some sort of bubble.
Everyone will customise their experience of the device, by adding what they like from the store.
My point is that, more often than not, these users won't replace core apps like Mail or Calendar - these apps work just fine for most people and there's no incentive to change.
Also, iCloud was announced in June 2011; plenty of todo apps had cloud sync well before that, when Apple simply didn't provide the service.
My case: ToDo: Wunderlist, now (Apple's) Reminders
Chat: Kik, now (Apple's) Messages
Photo editing (iPad): Snapseed, now iPhoto
Video chat: Skype, now FaceTime
The remainder of apps I use the native ones, given the iCloud integration with iPhone and iPad (Calendar, Address Book, etc.) Final note, I use Sparrow as my Mac client, but now way I would use it on the iPhone given the lack of push notification, that is simply a step backwards.
Bijan is not straight in this type of posts, where he is an investor, wants to be an investor and/or wants to give a hand to other fellow VCs. Anytime a VC says something about a company you just need to figure out his/her motives and incentives.
The question is; would I still do that if third party apps had a chance to interact better?
Stuff like opening files in another app just barely works. I can open an emailed PDF Dropbox, but Once it is saved in the right folder and uploaded (what I probably wanted), there is no way to transfer control back to the original app.
This should work more like the email/sms dialog that can be called from any app, and transfers control back to the app when it is done.