I like standards and abhor bloat, but I must admit there are GNU extensions that are so useful and well known that it would be difficult to do without. Probably

I like standards and abhor bloat, but I must admit there are GNU extensions that are so useful and well known that it would be difficult to do without. Probably this happens when POSIX specs are too strict or feature-poor to be of use even for medium-complexity tasks. One example is "make": I'm afraid that a POSIX-only implementation wouldn't run most Makefiles out there!