DirecTV did the same thing recently. They created two HD tiers - one with the HD versions of and SD networks they carry, and an extra $4.99/mo one that has the "HD only" channels.
When they did that, HDNet sued them because D* was contractually obligated to keep HDNet in the lowest HD-enabled tier. They settled, and D* moved HDNet into the lower HD tier, and moved HDNet movies into the upper tier.
I'm guessing that E* has the same contractual obligation, so we'll *probably* see HDNet stay in the lower $10 package.