re: B-52 Stratofortress, how is it still in service?

It fits a certain niche perfectly.
It's really still the cutting edge of design as far as big, reliable, heavy bombers with long range goes.

Need a bomber that can fly long distance while going undetected to drop bombs on a precise target? We have that too B-2.

Need an aircraft that can hit precise targets that aren't exactly that far away? F-15 strike eagle.

Need a flying tank remover? A-10 Thunderbolt 2.

In short it would cost a crap ton of money to design a new platform that can do what the B-52 already does and it wouldn't be much of an improvement.