The one page summary only works if you already believe it. The rest of it describes the research methodology that led to the disruption theory. He goes through many industries (OTOMH, disk drives, steel mini-mills, and ditch digging machines plus many more) to show how a new, worse technology served some new market, gained a foothold and customer base to build from, then improved to the point where it displaced the incumbent.

Think of PCs vs workstations, the iPhone vs Blackberry (the iPhone was a terrible smartphone according the the market in 2007, i.e. heavy email/business users), etc.

FWIW, I think the sequel, The Innovator's Solution, is a more useful book.