I think it's not so much about idealising anything...every relationship has its up- and downsides, they might differ a bit, but they are definitely there. If you ask a vanilla person what they get out of their relationship, they will probably idealise it too...they'd probably say the feeling of being loved, of having somebody to care for and somebody who cares for them, having somebody to rely on, etcetc. If you ask me "what do you get out of BDSM" the first things that spring to my mind are naturally not the frustrations and disappointments, the times it simply does not work or when life intrudes, or when I'm just plain outright unhappy with whatever relationship I'm having at that time.

I do think, however, that BDSM relationships differ from vanilla relationships in the level of trust and communication involved. Both, I believe, are assets most important, even intrinsic to BDSM relationships -- and whereas these are certainly good things to have in vanilla relationships, it's not something AS essential...you can do without these extremely high communication and trust levels, simply because you'll never find yourself in a situation where you have to trust as absolutely, or where it is so important to communicate your thoughts and feelings. But sheesh, I went on a tangent here, didn't I?