Well, first off, I think you are correct that the major concern is that
the paper could literally destroy a laser printer. The surface probably
can melt right off the paper and adhere to the heated fuser of the laser
printer, and that could be a permanent damage to it.
However, I do believe Epson is making yet another statement here, and
that is this paper doesn't tend to work well with other inkjet
technologies. For instance, it may be very slow drying with inks from
other printer companies (thermal inks) and if that were the case, the
ink might transfer to internal rollers and other parts, causing damage
to the printer and ruined images, so wasted paper. This disclaimer is
pretty broad, and it says that Epson doesn't recommend you use that
paper in anything but Epson inkjet printers.