I have used plenty of 2x DVD-R blanks on my Pioneer A03 Superdrive with no problems and I am loooking at getting a spindle of 4x blanks soon.
If 1x media is all you have then, well there you go; but depending on the MAC system or external DVD-R burner you have, anything up to 2x or 4x should work.
Sounds to me like an ancient history voodoo like it was in the audio industry a few years ago that the BIG BOYS used ONLY 2x CD-R burns to master from. All about BLER's or bit rate errors.