i'll take the contrary line of thought. if as you said the wheel does not turn after you removed from the bike i would suspect that it was either a bearing and/or hub/axle related failure. this is a rarity but has been known to happen albeit usually does not lockup wheel. i would ask the bike shop to inspect the hub bearing components to see if this is the problem. these wheels are somewhat lower in quality and may have had greater acceptable tolerances when built. if so i would think that shimano would want to know and would defintely make resitution to restore the bike to it's previous condition and be happy you were not seriously hurt.

please keep us posted and post pics if possible.