The companies all seem to be different on news leaks. Everybody seems to know everything that Sony is going to do several weeks in advance, Nintendo plays its cards very close and MS is somewhere in between.

I was wondering whether Sony leaks all of its news several weeks in advance on purpose in order to build up hype (basically viral marketing through rumours) or whether they are just really really terrible at keeping a secret.

What do you guys think?

Bit of both.

Look at for instance MS announcing FF13.

No-one had a clue before hand so if two big companies can keep something like that hidden it makes me think most leaks are intentional.
The PSPgo is another one.

Well i don't know but the slim rumors had every news/tech site finally confirming the slim so if it was on purpose i think it worked.

sony kept FF14 secret

With that I don't think there was much to keep secret, doesn't seem like it had been in development much. I'd say the FFXIII on X360 was similar too... I don't think MS had to keep the secret very long.

I would think the greatest reason secrets get leaked is Sony and MS have a LOT more employees than Nintendo, they are just much bigger companies.

Its intentional. Maybe Sony is really stupid though, its possible.