In terms of engineering staff, they are the exception, not the norm. A company like home depot or kelly moore paints would have a tough time relying on open source for all their operational software.
In terms of engineering staff, they are the exception, not the norm. A company like home depot or kelly moore paints would have a tough time relying on open source for all their operational software.
EDIT: I added Google because of robots, AI and driverless cars, I'm not really sure Twitter is on that level.
In terms of software engineering Twitter is absolutely one of the best around.
Is doing so wrong?
For vertical software systems, probably. For applications developed in-house, I'm guessing that even at Home Depot or Kelly Moore it's the other way around -- more and more, you have to make a good case for using a proprietary library. The connotations of "open source" have changed somewhat, and open source libraries are becoming the norm, even at large old-school software businesses, where the lawyers hate open source.