"Acquire venture funding" was not a 37 Signals goal. Ask most venture capitalists and that will be in their definition, though.
"Hire more employees" is arbitrary. Why is that a goal any more than "buy office chairs?" Hiring employees is a side effect, not a goal.
Ask someone who thinks single founder companies don't work and their definition will likely exclude companies like del.icio.us.
Ask techies, and startup means "a tech company" but personally, I would call Ben & Jerry's in the 70's a startup.
In terms of goals, sometimes the process evolves--like hotornot.com and the goals aren't there at the outset. Sometimes the goal is "build a better search engine" and everything else evolves later.
For these reasons, I prefer an inclusive defintion of startups, rather than something that means "startup like mine, or startup I'm looking to invest in"
I'd argue that 'scalability' is an important component of a startup though. I don't think anyone would consider a consultancy to be a startup - although many do meet your three criteria. They don't scale since there is an upper bound to revenue per employee (while a software product/website has no such bound).
Paying a college student $9/hr is a win-win in my opinion.
If you find college students who actually know shit about computers might they not have some other means for making better than $9/hr?
I have no idea what the market is like for these things, but I'm wondering if you'd be better off somewhat overpaying and making sure you had people you could trust to sort out problems when some repair routine doesn't quite work.