And the author explained in his FA that there's nothing wrong with that, but that he wouldn't hire you for his startup company. He wants the kind of programmer who is passionate about it, the one who wants to understand how things really work under the hood, how 3d computer graphics are synthesized, how you could program your own http server from scratch. There's nothing wrong with you wanting to work on the area that you think is the most profitable (I'm sure there must be some simulation/scientific programming jobs that pay more than any .NET job ever could), but the guy is basically saying that if .NET's the only thing you have to offer then he is not going to hire you for his startup.