I have ML Scenarios for my surrounds, and of cousre they work well with the Odyssey/Cinema fronts. However, I disagree with the claim that ONLY MLs work well - my previous surrounds were Triad Silvers. They are dipole cone speakers that are designed for in-wall mounting. They worked a lot better than you'd expect from all the discussion, with both my previous Aerius i's and the current Odysseys. Note that this for HT.
Matching for HT is, in my opinion, overemphasized, because on HT there is frankly little to choose from between the Scenarios and the Triads.
However, I do have a little bit of surround music (several DVD-As and a handful of SACDs) and there the difference is much greater. For surround music I might well agree that only the MLs will match ML mains.