The DVD player absolutely helped it's sales early on.
You're making the mistake of only comparing prices in the U.S. What about other countries? DVD prices were crazy high at other places or even very hard to find in some of the lesser developed countries but it was easier and cheaper to get a PS2.
Also check PS2's sales in Japan for the first week and compare it with the software sales and that will show that quite a few early purchases were for DVD only.
No one can know for sure how many bought it just for a DVD though.








