I dont think they are lazy and stupid per say.. I think the problem is that if you look at a keyword like online casino for example, there will be millions of relevant pages. So if you look based on content alone, there could be thousands of unique pages, each matching exact criteria in terms of readability, relevance, keyword density, etc. So there has to be another factor to base it on.
With links it gives them the opportunity to factor in so many other variables, like taking into account the thousands of linking sites and crunching the relevancy of those pages with the algo. There is just too many pages on the net to do it without links. I cant imagine another way for them to process value other than to randomly rank sites based on nothing.
Just my opinion 