I think it's a safe assumption that search isn't broken, it's just presented whatever way optimizes revenue while still using your choice of sort column as a guideline to keep it from being too blatant a lie.
It's broken from a usability standpoint. "Search by average stars" will give me pages and pages of 5-star products with tiny numbers of ratings before I'll see what I really want: a product with 1,000 ratings and an overall rating of 4.9.