In the grand scheme of things.. I couldn't see that it would end up costing any more...
sure, i agree, it won't cost you any more, but i just think that if you put the new ones on the front, then you probably aren't going to need another pair of fronts for about a year [talking FWD here], the rears may scrub away a bit on the inside but they last ages. if you put the new ones on the back, the fronts will be gone much sooner [probably, but not always], and provided they looked after you, mr average motorist will go back to the same place for another pair. result!
at least we have the choice of only buying single tyres. in france on holiday a couple of years ago my old Jag had a puncture on a rear tyre, a big one, near to the edge. i went to the local halfords type store, and in pigeon froggy explained my problem. a mechanic had a look & confirmed it couldn't be repaired [i think that's what he said..], so i asked if i could buy a new one. they only stocked Michelins - 95 euro each - bit of a dint in the holiday budget, but ok, i said, i'll go for that. but NON, monsuir, you have to buy a pair, as the car had pirellis all round, and it is illegal to have different tyres on the same axle. i said no ta, and put my space saver spare on & drove like miss daisy for the rest of the week.