First off, no, you don't need a "cadillac bow" to kill deer. Pretty much any bow 35lbs or more with 24" or more draw will kill a deer at 30yrds.
That said, yes, there are distinct advantages to shooting higher quality bows, and for those reasons, I tend to agree with the mentality "buy the best bow you can afford". I would say the same about a rifle, a scope, an E-caller, a truck, pair of workboots, socket set, etc etc.
Cheaper bows are generally less efficient, louder, and rougher drawing (which both hurt efficiency too). They'll also be heavier and generally longer ATA.
Personally, the efficiency of higher quality bows is worth the price. I paid $90 for my first bow, an early 80's model Oregon 80lb, killed dozens of deer with it through high school and college. Then once I had a good paying job, I jumped up to a Solocam, then a z7, and today I shoot a 2011 Bowtech Destroyer 350 and a 2010 Mathews Monster, and my wife runs a 2012 Mathews Jewel 50lb, into each of which I have wrapped up about $1800, not including shafts or heads.
My best friend and my brother in law both run 2012 Diamond Outlaw 70lb's that I played "bowtech" when they were kitting their bows (used to get paid for it, now it's just a hobby). Another buddy just picked up a new Bear Domain that we ran across the Chrony a few weeks ago when we put in his peep site.
Here's a quick comparison of the bows that I have written down in my chrony book:
Diamond Outlaw 70lb x 28": 413grn arrow at 262fps = 63.0ft.lbs.
Daiamond Outlaw 65lb x 29": 375grn arrow at 268fps = 59.8ft.lbs.
Bear Domain 70lb x 27": 408grn arrow at 254fps = 58.5 ft.lbs.
Mathews Jewel 50lb x 24": 360grn arrow at 243fps = 47.2 ft.lbs.
Mathews Monster 70lb x 28.5": 433grn arrow at 277fps = 73.8 ft.lbs.
Bowtech Destroyer 70lb x 28": 393grn arrow at 323fps = 91.0 ft.lbs.
Relatively speaking, the higher priced bows are getting a lot more out of their power strokes than the others.
Drawing the SAME WEIGHT AND LENGTH, I'm getting 50% more energy out of my Bowtech than my buddy gets from his Outlaw, pretty consistent with what the other Outlaw and the Domain are hitting.
What does all that mean? Faster arrows mean better range, and more energy/arrow weight means more penetration for long range kills. My Destroyer has basically twice the effective range of my old Oregon bow, with a lighter draw.
Do you NEED to be able to kill a deer at 70yrds? No. Do I want to be able to? Yes. I don't want to be limited by my equipment, and I can shoot well enough to kill a deer at 70yrds.
That said, I HIGHLY recommend the Diamond Outlaw as a "hunter's bow". Easy to set up, easy to tune, smooth drawing, great price, and pretty dang fast for a $500 bow. But, no, it doesn't stack up to the more expensive Destroyer or Monster.
The Domain (like most Bears) is one of the quietest bows I've shot.
