Simply being 'loyal' to a local store doesn't have an answer. I'm not sure I've ever been completely loyal to a particular store simply because it is there, but preferring to spend a little more (in some cases at least) because you like the service from a local store is a valid reason, I feel anyway. As to why they will be more expensive there are many reasons. Bulk buying and supplier discounts I've mentioned but the other fact is that having a retail outlet on the high street is VERY expensive. Staffing costs, rent, rates, heating, lighting, maintenance........this all adds up and if the store is to make a profit - they are there to do that at the end of the day whether we like the idea or not - the price will be higher.
Do we need a high street?
Should we all make the savings and buy online from the cheapest source for all of our needs?
Should the suppliers support the high street more, it is currently a very good outlet for their goods?
Personally I prefer to buy from a shop where I can go in, see what I'm buying, talk to staff, get it there and then, be able to pop in with questions and be able to physically take it back should something go wrong. I may pay more for this privilege but for me personally that is something I'm willing to do.