Probably true, but being successful without a diploma still takes some luck.
A good example might be Josh Parnell, the developer of Limit Theory (URL:http://ltheory.com/).
The guy seems to be quite brilliant, and I believe he is capable of pulling off his plans for a space game with an unprecedented amount of procedural generation. But he still got lucky in finding enough backers for his Kickstarter.
Another thing we can learn from Josh's example is that it may not be necessary to drop out of college. He wrote that he put his studies at Stanford on hold, with the option of continuing later.