I've read the same thing, other than the blurb on the Purolator site there is nothing that shows that they should not be used. Some of the antiquated twins (HD) have very low pressure oil systems, (maybe because HD is typically dry sump?). From what I have read that was the reason for the warning on automotive filters in general.
I've been running PL14610 or 12's (depending on what I have laying around) for years. The only bikes I did not use them on were my Suzuki's (different thread pitch). It's the same filter I use on my 675 track bike, in my WRX and in my mom's Nissan.