If we were to lay out a line and on the left end put B2C, and on the right end Enterprise B2B and ask where the mentality of Growth is being applied first and where it can be of the most value, it would certainly be on the left end of that spectrum. Facebook, Twitter, Dropbox, etc were the first to really form these types of growth teams for a lot of reasons. Today, if you are a B2C company and not applying this mentality you are behind.
That being said Growth is quickly moving into the right end of the spectrum. First are freemium B2B products like the one I'm working on: http://GetSignals.com
. There are some B2B SaaS companies applying some of these techniques and processes. Thats largely due to the "consumerization of the enterprise" trend where companies are applying consumer techniques to make their funnel more efficient.
Over the long term I think the number of companies with large enterprise sales cycles today will be fewer and fewer as adoption models of enterprises change. In the interim I think growth teams in those types of companies can be applied to identify and remove friction from the cycle using technology. Ultimately though the longer your customer cycle is and less amount of data you have (and thus the longer the experiment cycles) the less useful Growth processes will be.