It's too simplistic to focus on price alone in yourcomparison. You have to take population stats and a SWAG at the number of loyal, dedicated collectors (of SGC vs. PSA) into consideration, as well.
I am currently buying PSA-graded 1969 Topps commons (all are graded mint 9), in hopes that they will cross over to SGC 96. I admit that's a huge gamble. But the point is, I'm paying $20 or less for these (PSA) cards. The last batch of SGC-graded 1969 Topps commons (mint 96) that auctioned on Ebay (dhcards last Christmas auction) sold in the $55 to $99 range. Some, that were highly sought by several collectors, went for much, much more. And BTW, when I say "common," I mean players you haven't heard of before.
Bottom line: too few comprably SGC-graded cards with even a few die-hard collectors slugging it out to acquire the card will drive the price up to otherworldly levels. It makes the PSA-to-SGC crossover experiment worth the gamble.
So, to answer your question, the price differences could result from any of the following:
1. SGC kicks a$$ and rules!!
2. There are relatively many PSA 9 '77 Pete Rose cards available and relatively few SGC equivalents.
3. There are relatively many '77 Topps PSA collectors and relatively few SGC equivalents.
4. Those PSA '77 Topps collectors already have a highly graded Rose while the SGC guys are trying to outdo each other to acquire the SGC equivalent ... (is the Rose a 1 of 1?). Therefore, the competition for a PSA 9 '77 Rose is less.
2-4 are just variations on the Law of Supply and Demand ...
Old, dense-headed hammers are cool. Best nail pounders.
In my mind, $150 and $162 are basically the same price. Someone probably fell asleep on the first auction, woke up mad and had to bid a bit higher. You can't read anything into this...what are the historical numbers for each of the card grades? -- then maybe you can make a case.