Yes, it is true that some folks have quite a bit of trouble with those (thermostat) connections. Some of those connections are so corroded that there is essentially no hope of separating them. Others say you can cut the lines off, or at least the big nuts, but of course that destroys the oil line. All I can say is to be careful if you're gonna cut your nuts off.
I am going to try to remove one of my lines from the thermostat, but I will not risk breaking the thermostat and I would destroy the line only if the new line will fit, which I don't know yet.