Can an iPad user view a flash site? No. Apple's lawyers and control of technology prevent that. No matter how much the person who paid for the device wants to, they can't.

Does anyone "have to" use Flash? Absolutely not. Sites can be developed without it. Sites can offer plain-html versions. People can decide not to visit the sites. Personally, I use the No-Script plug-in for performance reasons, and I don't bother to load about 80% of the Flash objects. Because.... I don't "have to." But I can. iPad users can't. iPhone users can't. Droid phone users can (some versions now, all in 2.2).

Flash works pretty well across browsers (when Steve says it's OK), but attempting to achieve the same results with four major and a half dozen minor browser vendors, not to mention browser version numbers? That's going to be hugely annoying and QA expensive.

By the way, I haven't heard Apple mention QuickTime or Microsoft mention Windows Media in their jihad against "proprietary" video. They're squawking 'open standards' after their own proprietary systems lost viable market share. As of March, Safari has 4.5% market share. How much time ($) should web sites spend attending to its quirks? Much easier to do one Flash implementation.