rent to own ratio

So, I'm reading an article from the new york times written in 1999 about murray hill, and it reads: MEDIAN PRICE OF 2-BEDROOM CONDO: $450,000. MEDIAN PRICE A YEAR AGO: $400,000. MEDIAN PRICE 5 YEARS AGO: $250,000. MEDIAN PRICE OF A 2-BEDROOM CO-OP: $350,000. MEDIAN PRICE A YEAR AGO: $350,000. MEDIAN PRICE 5 YEARS AGO: $200,000. MIDRANGE RENT ON A 2-BEDROOM APARTMENT: $3,500. My question is: if rent for a 2-bed was $3,500 then, but price of a co op was $350,000, why has the rent-to-own gap/ratio widened so much? Also, have co-ops closed the gap with condos in terms of pricing (they don't seem to be much less now than condos)? Is there an earlier thread that explains either or both of these 2 things? Thanks!!