Just moved my startup(www.getpei.co) from Los Angeles to Austin for an accelerator and can attest that software is sprawling! There are tons of great meetups supported by a ton of great innovative companies and with amazing events like SXSW (which will be our first) they environment is growing for engineers.
The reason I see this happening is because I believe with the roots of live music in Austin, there is a lot of creativity growing around here. When you mix it with effective development and adventurous culture, there is a great mixture of support systems to really build a software-based community.
Weirdly enough, my company is actually looking for a CMO now in the area, and we are finding it difficult to fill the position at an early stage company. So shameless plug, if you are in the area ( which I am finding a lot of Austin is HN), please feel free to reach out!