haha this is an OLD thread, but ill still try and help you.
yes, there is definatly a difference with DH and hardtail. you can ride exactly the same stuff on both, but with a FS, theres alot more room for error, and a hardtail, your more likely to get bucked if you screw up lol. but it does force you to learn to ride much smoother.
as for a bike for the shore, hardtails are definatly fine. in fact, i find them better, cause you can do more jib type shit. hardtails get squierrly on real fast rocky DH. for slow NS style stuff, id say you get more control.
as for frames, ive been incredibly stoked on mountain cycle. the old 04 rumbles (what i have) are great bikes. the new ones have a much improved drop out system that allows you to run all sorts of axle configs, and its a much burlier  derailleur mounts, plus thru-axles. Evil Imperials are rediculously sick, but pretty damn expensive. Specialized P2s are great bikes for these applications, as are banshee morphines, etc. there are plenty more. if your on the cheap, i know you can get rumbles for absolutely nothing (like 250 bucks off greenfish), and they are super nice bikes, great geometry, awesome welds, and nice lines. id have no problem recommending them.