Danny Greenfeld notes that large parts of his personal development stack are proprietary, even though he's a huge open source enthusiast and promoter: http://pydanny.com/thoughts-on-my-stack.html
I think it's OK. If we try to do everything from scratch ourselves, we'll spend all our time on that instead of working towards what we actually want to achieve, and sometimes other factors are going to win out over the importance of the freedom to tinker.