Both have their ups and downs, but broadly speaking, private money tends to be a lot more flexible and risk-liberal, whereas public money can be like having the worst aspects of the ignorant absentee CEOs-golf-buddy manager and the micromanaging hands-on desperate-to-prove-himself CEOs-nephew manager.

Public money is eventually traced back to some elected official who has absolutely nothing to do with technology but is also very emotionally-invested in showing to the constituents that the money isn't being wasted - to the point where spending the money on something useless but concrete ("ergonomic" coffee mugs) might be deemed preferable to a long-term investment that falls on the wrong side of a term-limit.

Again, public money can be fine and completely no-strings sometimes (and, conversely, private charitable contributions can sometimes end up with plenty of strings too), but there's certainly reasons to point out the differences.