As of January 2013, 78 of the original 744 B-52 aircraft were operational in the U.S. Air Force. (All are B-52H models.)
https://en.wikipedia.org/wiki/Boeing_B-52_Stratofortress
The USAF had 66 B-1Bs in service in September 2012, split between four squadrons organized into two Bomb Wings: the 7th Bomb Wing at Dyess AFB, Texas, and the 28th Bomb Wing at Ellsworth AFB, South Dakota.
https://en.wikipedia.org/wiki/Rockwell_B-1_Lancer#B-1B_program
A total of 20 B-2s remain in service with the United States Air Force, which plans to operate the B-2 until 2058.
https://en.wikipedia.org/wiki/Northrop_Grumman_B-2_Spirit
78+66+20 = 164 strategic bombers of three different generations in service.
An 80-100 unit acquisition program represents a 48-60% replacement of the existing force.
If you just count B-52s and B-1Bs, the in service numbers drop to 144 and the replacement percentages go up to between 55-70%.
If we use the 14 aircraft per B-1B squadron as a nominal per squadron target, 80-100 aircraft equips 5-7 squadrons. To maintain operational capability equivalent to four B-1B squadrons, you can go as low as 66 aircraft. Strategic plans, the need for operational rotation of units, and maintenance/overhaul/rebuild planning establish the requirement for multiple squadrons. There also have to be a certain number of aircraft in storage and available for R&D purposes.
ASSUMING the B-52 component is just going to be retired without replacement and that the B-2 bomber capability replacement will be the subject of another program, the 80 aircraft purchase is probably the lower number needed to maintain USAF strategic bomber capability equivalent to the existing B-1B fleet.
The USAF, if it can keep acquisition costs contained, will probably get 80 aircraft. Anything above that will be a bonus.
“... if it can keep acquisition costs contained ...”
That’s a very BIG IF ... and more than likely will become an aerial ‘jack of all trades’ like the F-35.
And remember, the cost of feeding the homeless will increase in direct proportion to the decrease in size of the AF and its budget ... and thus, the ever-shrinking number of new aircraft with an ever-increasing cost per unit. Ipso facto, the 8-10 number remains a distinct possibility.
Back in the late 1950s I was an engineer at Wright Field's Armament Laboratory. We were developing a new bombing-navigation system for the B-52. General Lemay claimed he couldn't spare any of his new B-52s for testing the bomb-nav system. So we tested them on a B-47. Unfortunately the B-47 had a lower ceiling than the B-52. When the system was eventually installed in B-52s and taken to altitudes higher than we could test in a B-47, the electronics arced over because of the lower air pressure (lower breakdown voltage). We eventually got that fixed, but it impressed on me the need to test in actual conditions. I insisted on that for the rest of my career.