I build stations for a living, we have contracts with all the big oil company's. Yes all stations have blenders to mix 87 & 91 to make 89.
Each station is a different scenario, some are privately owned (dealer branded "Joe's gas & save") He most likely almost never buys from the same refinery. Stay away never know what your getting.
Then there are the common named brand stations most of these are owned buy a large Corporation and are mandated by that brand to use isolated refineries.
The only "Big Name" oil company that owns there own station now is Chevron, but probably only 30% of them are actually corporate.
Your comment about pricing is 100% accurate, its all about projection and inflation.