That people cling to tradition for irrational reasons. Also, one valid reason is that they might want to print your resume. It's a lot easier to print a PDF than a web page.
There's nothing irrational about it. If I ask for a resume, it is because I am looking for a resume, not a pointer to where I can go find a resume.
Perhaps I am collecting all resumes received by email into one mailbox, and I periodically do a batch print of everything there, then take the printouts home to review in comfort on the couch.
Perhaps I'm doing some classification of resumes based on keywords in the body and attachments, and the software that does that does not follow links.
I've dealt with agencies who can't even handle a PDF file because it's unsupported in their internal systems, and yes, it's really 2011. It's basically Word or nothing.
In the end, my view is that smaller companies or startups are probably more receptive to a Linked In profile than larger, more established companies.
I think that's subjective. I've used mine (successfully) as an informal resume before. With all things job hunting, you approach is going to be dependent on the organization you're going after.
That people cling to tradition for irrational reasons. Also, one valid reason is that they might want to print your resume. It's a lot easier to print a PDF than a web page.