I remember several years back, one of the main things I looked for in forum software was the ability to have forum/subforum nesting, with no limit on how deep it could go. Very few packages offered that, with IPB being one of the few that did. Notice how it's rare to find a package that doesn't support that concept now? Took them awhile to realize just how useful it is.
There will always be a bit of 'theft' of ideas, but it's how we progress. I'm sure there was a point when it wasn't possible to lock a thread, you had to delete it. If each forum idea that was created was to remain only with that original software, then forums today would be a total mess. It's sort of a necessary evil, to take an idea and implement it. vB does it, IPB does it, SMF, etc. But to almost CLONE the entire thing is just pitiful.
Ideas and trends do tend to get recycled though. In another 10 years, the layout (concept) of IPB1.3.x might be considered cool and "in style". Not the old style exactly, only the layout of it. Look at the Mustang, it's taken on a look that has resemblance to the 1960's, while still being noticeably different.
Just how things are.