During Windows XP era, first thing one do after installation is to use IE to download all sort of alternate apps like Firefox, Outlook/Thunderbird & Gtalk client. Same continued even when updareded to Vist and then to 7. Though IE improved a lot over time. However when I moved entirely to OS X nothing of that happened. With Snow Leopard Safari worked fine, Address book was functional and syncs fine with GMail, iChat can connect to Gtalk/Facebook, mail client worked fine with IMAP/Exchange with no conversation view and not much keyboard shortcut friendly. Unless someone is looking for an special functionality 3rd part application isn't required at all.
Things changed a lot with Lion upgrade. Safari doesn't provide smooth experience and will refresh page every time you hit back button. It'll also hange every now and then. Address book got the worst UI refresh. Mail client got little better with conversation view. And lastly iChat reamined the same. Yeh, iChat got plugin support which no one writes. iCal might be an exception as I like it better than in 10.6 though I use QuickCal most of the time and Remember the Milk primarily.
All of these made me look for alternative. Apps that get the works done without crippling the UI. Replaced mail app with Sparrow, cobook instead of address app and Chrome instead of Safari, RememberTheMilk & QuickCal instead of iCal.
All of this raises an question is OS X entering an era where people look for 3rd party apps and no more rely on Apple for bundled apps? Well executed Mac App Store will help this a lot. Or is it just an phase where few user don't like Apple's design but will eventually get along?
It's hard to say. May be these apps will improve over iteration but use of 3rd party apps instead of bundled apps will be on rise.