These are definitely beers to have when you're just having one in the night, lock them away if you're having a session. I remember when Little Dove came out people made a big deal about how they'll knock you on your arse if you're not careful. Now beers in the 8-12% range are fairly common.
A mate of mine who's in the industry told me the reason why stronger beers have become more popular. Basically, it doesn't really cost any more money to brew a 10% ABV beer than it does to brew a 4% beer. He said (I believe) that the cut the government takes in tax is a flat rate, but when it comes to what people will pay for beers, they'll obviously pay more for the strong beers than they will for a standard or mid strength beer. So you can make more profit selling stronger beers than you can with lower strength.
Must say that the increase in strong beers has really made me appreciate a good session or mid-strength beer.
I think there's a bracketed ABV tax allocation there that does rock the pricing boat a bit, but I don't believe it's as broad as 4-10%. It could have changed, though. My discussions with brewers was more along the lines of if they were going to brew a high ABV beer they'd go all out on it and make sure it was worthwhile and going to sell well because they were creeping into a higher tax bracket.
Depending on style there is also the increased cost of production, head scratching ****ery with trying to nail the fermentation so it's actually drinkable, increased risk of needing to drain pour a batch you've invested a lot of time, grain, hops into it.
The more profitable high ABV beers would be the dark beers I reckon. Minimal hop schedule. But then if you want to charge a premium you introduce barrels, and up goes the brewery costs.