This is so true, Ahmed. I've been highly irritated by this question for a long time. There is always more to it (see other comments - branding, market expertise, 'better' product, blah blah) but at the end of the day, anyone can innovate.
Agreed. LinkedIn's been awful for a long time and unfortunately nothing has paralleled its popularity... hoping something that doesn't suck will come up and sink it into irrelevance in the abyss of the interwebs as Facebook did to MySpace.