SVHS tapes are high quality. The shell has a hole in it so that the machine can recognise that it is an SVHS tape.
All machines wear out if left in pause mode. Therefore they switch out of this mode after a few minutes. Pressing the ET button just lets it know that it is a normal tape and enables the SVHS electronics to come into play, hopefully, tweaked for ET or we've been ripped off for years.
I believe different heads can be made from different materials. Panasonic used to imply that their top of the range heads were made from superior materials than their lesser models, but did not imply they would wear out quicker. Therefore, it is just possible that ET heads, which have to record higher frequencies than ordinary heads, have to be made from a lesser wearing material, but I doubt it. More likely, an inexact translation from Japanese. I believe that there should be no difference in the wear of any machine if used in the same way.