While I agree with your second assertion, I would think that most companies would prefer to have on-premises hosting for their intellectual property. Github and Atlassian offer this.
My impression is that many large organisations would prefer that, but most small organisations would prefer to outsource these kinds of things if possible. From a perspective of how much money you will make, I think focusing on the small organisations will be better. The economies of scale just don't kick in until you have a couple hundred employees (or more!). Especially from the standpoint of security, most small organisations simply can't hire the staff they need (couldn't afford them even if they could find them). So there is a solid market need there. On the other side, large organisations have the skills they need to roll their own if they choose, so your business plan has to rely on walking that line of offering software/services more cheaply than these big organisations can do for themselves. Personally, I think that long term this will be a losing battle. Although Github has a strategy for large businesses, I think they are better positioned to service small businesses. For this reason, I much more bullish on Github than I am Atlassian (which seems to tie their horse to enterprise at every turn).