Motorhead are on this tour because Lemmy and Dave are good friends. Motorhead have no shortage of touring invitations, and Foo Fighters could take virtually ANY band out with them as it wouldn't make a lick of difference to their ticket sales. On top of that throw down the fact that Foo Fighters are probably the BEST radio rock band going, and one of the very few who have neither sold out their sound, or sold their souls by way of reality tv or constant bad publicity. Hell Dave has gone on record saying that he never intended for the band to get famous cuz he hates the band name, he just had these songs laying around so he recorded and released them after Nirvana died so he was at least moving forward musically.
This is honestly an ideal pairing for both parties, and is a rare occurence where both the support and headliner on an arena tour are worth the ticket price. Us Europeans will probably get Twin Atlantic or some other trendy band, so count your blessings.
Yesterday don't mean SHIT.