I don't get why people think Luvdisc and Mamanbō aren't related; sure, you won't have Luvdisc around, but why wouldn't Mamanbō be available even if it evolves from Luvdisc? It wouldn't be the first time that you find a wild evolved Pokemon but not its previous form. I can't recall any specific examples, but I know it's happened before in previous games... In any case, I think they're definitely related (it's too much of a coincidence that they're so alike and they have that whole Healing Heart thing going on; I'm willing to bet Luvdisc will have Healing Heart as an alternate ability in BW, and then when the BW remake is made, Ludvisc will be made available like it happened in Platinum with a few Pokemon whose basic forms weren't found in Sinnoh).
*shrugs* It all makes perfect sense to me. :>