[lmz]

Of course that depends if the optimization was compiled into the version they have. One can imagine two binaries with the optimizations just missing from the free one.

[rkangel]

If they distribute the one with optimisations, then they need to make the source available.

[Tuna-Fish]

... but only to the ones they distribute it to. They can then choose to redistribute it if they want to.

[lmz]

... a.k.a. the RHEL model (with contract termination on sharing source).