Dare Obasanjo comments that Amazon et al are huge "enterprise" applications and so what is all this complexity bullshit that Enterprise Architects talk about. I agree that these web based applications are huge however they are fairly modern designed systems which were built from the ground up with scale in mind. Many (if not most) applications in enterprises were built a long time ago with no concept of their present use and tying these together is complex. Additionally businesses which are not as focused on one product line / one channel have much more complex organizational structures and politics to navigate, a point I feel Dare probably understands as he too works for Microsoft.
Both points are nicely made by Stefan.
I do agree however that in many cases these problems are made more complex by consulting firms who are looking to make money from the complexity; a pet peeve of mine.