I agree if you mean more than just a financial incentive. Job satisfaction at Space X must be extraordinary. G4S on the other hand is a company whose business plan is to sell 'security theatre'. They hire and train people for the minimum amount possible and resell that for the maximum amount possible, they don't have any incentive to care about their employees. They are just a HR department that processes people applying for and leaving jobs as efficiently as possible and a sales department that sells that time. No one is going to take pride in their work for a company like this. Maybe they made a mistake in assuming that there were an enough desperate unemployed people available to fill these positions?

I think that successful organisations, whether they be state run or private companies, depend massively on the character of the individuals that run them. I expect that Space X is successful because Elon Musk is a very rewarding person to work for. And for an example of a state run organisation like this see Frank Pick[1] who, as manager of London Transport, untangled the mess of privately constructed transport systems and made it into the poster child for public transport systems across the world. Pick's organisational values and culture outlasted him for many years, even today new transport projects in London have to be pretty high quality because they are measured against the legacy of all the great stuff the was designed and built in the 40's and 50's.

[1] http://en.wikipedia.org/wiki/Frank_Pick

SpaceX is an excellent example of outsourcing working well.

But G4S had the incentive of a £300 million contract, and their CEO gets £830K/year, and they still couldn't get it right.

I would argue that SpaceX's success is much more tied to the founder's vision than to any kind of monetary incentives from the government.

I personally suspect that the real mechanism is not private vs public, but rather organization structure and leadership style.

SpaceX is led by Elon Musk, 'nuff said.

SpaceX are well-known for not using subcontractors to make their parts etc. They do almost everything in-house.

Does spaceX even outsource their security guards?

Yeah, unlike policing and health, SpaceX's activities are not necessary. Don't get me wrong, what SpaceX is doing is fantastic, even inspirational, but not an essential service. So, if it goes wrong, even badly wrong, it really does not matter.

I don't see how "unnecessary" or "necessary" matters, as long as we're talking excellence.