If my understanding is correct which I'm not sure it is. A Prime Rib Roast is cut from a Ribeye just as the Whole Beef Rib Roast is but the Prime one is cut from a Ribeye that was graded as Prime instead of select or choice. Many people will call a Rib Roast a Prime Rib Roast even tho its not Prime grade. One of the ads is also bone in and the other is boneless. Around my area its unusual to find a "Prime" graded rib roast since they are more expensive generally
If they're both choice, or both prime, the only difference is the price (and bone in/no bone)--in my book.
I just bought 4 "Choice" standing rib roasts (avg 5.5 lbs) yesterday for $5.99 per pound (bone in). That is me stocking up for a few months at the best price I've seen in my neck of the woods in years. I got 3 last year for that price too (smoked the one and was better than any "Prime Rib" I have ever had).
Most of the time around here, the standing rib roasts are "choice" bone in, and the "Choice" Ribeyes are cut into steaks, without the bone.
The best price I ever see around here for them is $5.99 for the "bone in" standing rib roast & $6.99 for the Ribeye steaks.
If those are choice or better, I'd take a freakin' wheelbarrow to that store quick!
These are both cut from the standing rib roast. The word "prime" in the so called "prime rib" is meaningless as pertains to quality grading. The USDA allows the use of the term "prime rib" for a standing rib roast,regardless of the quality grade of the carcass from which it is obtained. The "rib eye" is simply a portion cut from the standing rib roast and the "rib eye" may be cut as a roast or as steaks.
Now I have always thought that they were the same hunk of meat and I'll take all of those 2.98lbs roast that they will let me have. Winn Dixie here in Fla had them for 3.99 lb bone-in rib roast and I got 3 whole ones before they said I could have anymore. So I went back later that night and got another one.