[zmmmmm]

> I don't understand ...

Start with your assumption that drawing on something you saw to make something better of your own is inherently wrong. Many people just don't share this assumption of yours. In fact, if many people did, Hacker News and ycombinator would be a very empty and lonely place - just look at all the startups: 99% are "some existing idea where we have made a small and novel tweak that makes it better" - PG even openly encourages startups to pitch their ideas that way (we've made X for Y). The top link right now is gist.io and the entire page explaining it is about how similar it is to a bunch of other services but they've made it slightly better for one special case. And the comments there are all favorable, nobody is shaming them for ripping off somebody else.