That makes sense. The oxides of the solder could very well have a far higher melting point making them immune to the thermal output of a standard soldering iron. That is an annoying problem, not enough heat it won't melt, too much heat and the board itself could be damaged.

I looked at the pics in the thread you linked. You're lucky the crappy caps didn't damage the legs on the nearby ICs. The caps in the Classic II I got not too long ago caused severe corrosion on the legs of several ICs, some as far away as a inch or more from the cluster of caps that went bad. I'm still debating whether to just ditch the logic board and get another one that is in better shape or try recapping/repairing this one. The external SCSI port is also crap, completely rusted.