A typical n900 user has Skype, SIP ip-telephony, MSN, ICQ, facebook, web server etc. all running while the phone is in their pocket.

For a comparison with what other modern handsets are running while tucked away: (Kernel mode doesn't count)
winCE: nothing
iphone: nothing
symbian: nothing
android: nothing / in 2.2 it became possible

This means that n900 is the only phone so far that has fulfilled the instant messaging needs of the younger generation.
If the market missed this, it's hard not to blame marketing or company steering.