It's like making a cake... you can make it from scratch or you can buy a box of Betty Crocker mix.
While I agree completely with the sentiment, I will have to politely disagree with your specific example of Betty Crocker cake mixes. For most people, they'll have better success with the boxes mix due to conditioners that are incorporated that are generally not available to home baker's.
But this does bring up the issue of ingredients. Yes, you can buy the exact same malts, adjuncts, yeast and the like and make the exact same recipe without the kit, however you have the freedom to modify, too. On the whole, the kits include mostly US-made malts. At least that's been my experience. If you're making a British ale, you might want to swap Briess 2-row for Muntins, Thomas Fawcett, or another British-produced pale 2-row malt as an upgrade.
Regarding the local homebrew shop prices, yes, they will undoubtedly be higher, but within reason I try to buy as much as I can from them. In spite of having a significant inventory of ingredients, it seems I'm always needing a ounce of this or a pound of that, a length of hose, or a CO2 tank swap. Liquid yeast in the summer is a risky thing by mail. Finally, if you buy sacks of grain, the price can be very competitive locally after taking into account shipping. Keep em in business!