Quite the contrary.
Forum and Articles --
There was speculation here back before the iPad came out, over whether or not it would allow running multiple iPhone apps at a time.
When it did come out, articles were written about this inability, such as this VentureBeat article listing the lack as a #1 reason not to buy an iPad.
Apps to Pretend --
To get around the lack of multi-window support, some iPad apps were created (as much as Apple would allow) to emulate the ability.
E.g. dual browser window apps, and the Taposé app that tried to be like the Microsoft Courier.
Competition Does It --
Samsung's Note tablet allows having not only overlaid little windows, but some of their apps are made to work side by side. Have you never seen this commercial of what the Note can do with side by side windows?
YouTube: video
Or Microsoft's recent ad where Siri says "I'm sorry I can only do one thing at a time":
YouTube: video
It's like anything else. You don't have to use it. But sometimes it would be quite handy. Have you never wished you had a calculator onscreen while looking at some figures? Some people don't do a lot with their devices. Some of us do.
You know iPad runs iOS, NOT windows, yeah?