I don't think every spot of rust at the welds indicates a pending failure as every sled I have owned in the 32 years of riding has always shown the first place rust will start is at the welds. But I do agree they do warrant inspection and the rust may actually make it easier to spot a crack.
I think the rust has to do a lot with sloppy prepping of the part prior to painting. Since the welds are typically rough and uneven with nooks and crannys it's difficult to get full paint coverage thus leaving some exposed steel. Also if the weld isn't cleaned properly the paint will have a difficult time bonding to the metal and that to me seems to be the reason the paint flakes at the welds.
