but, also wasn't all the serum that was left used to make Cap?
It's been a while since i've seen one... but I was under the impression that it was a limited order type thing.
An early version was used on Johann Schmidt and turned him into the Red Skull. Erskine perfected it, possibly with Howard Stark's help, and used it in conjunction with whatever Vita-Rays are on Steve Rogers. Erskine was killed, but enough samples of Rogers' blood were taken we presume Stark was eventually able to recreate the Serum (or something very like), which HYDRA took, and killed Stark, taking the secret with him. Zola never knew the whole thing, so he couldn't fill in the gaps, and those other five Soviet Super-Soldiers are it. P.S. We are still unclear on what Zola might have done to Bucky, both before Steve rescued him and after he fell from the train.
Anyway, after Howard Stark was killed, Bruce Banner was trying to recreate the Serum for General Ross. I assume he tried gamma radiation because no one surviving knew what Vita-Rays were. We know how that went.
So there's been a lot of Super-Soldier-y stuff done to folks, but yeah -- Steve is the only one exactly like Steve (even if the Soviet ones had the Serum right and the process was perfect, they were nasty people who became uncontrollably horriffic -- pretty much the antitheses to Steve).
--Jonah