The patent US7975000 describes a specif way of doing A/B testing.
This means that it is that specific method which is patented, and anybody who creates a different method may be free to implement, sell or patent it in it's own right as long as it does not conflict with the specific method already patented.
The evaluation of if the second implementation is violating the patented method needs a subject matter expert. The onerous is on the patent holder to exercise their right to the patent, so if they don't do that out of philosophy or ignorance then other people can get away with implementations which potentially could violate a patent. Many tech giants has a 'defensive' strategy in their patent portfolio where they aim never to sue anybody unless sued first.
Alternatively a patent holder could also license their patents and get right to implement the invention in their own environment -- this famously happened with Amazon's one-click patent.