If you have a quirky stdlib, this can be a big problem if its source is visible. This can be a tremendous source of bad examples to the community. This happened with the various Smalltalk images -- there was some rather good code, and then there was a lot of procedural/spaghetti code by junior programmers. A lot of it happened to get into places where it would be very visible to other junior programmers. (Database/OR tools.)

I think that a lot of this quirky stuff is due to the "uncool" factor of cleaning up such infrastructure level stuff. It's much cooler to be working on a proxy framework that talks to some new protocol. Making sure dates and times work well seems pedestrian. But it is actually tremendously important.