Err.. but they are rolling their own tracking service + ad exchange. They say they will create user segments that advertisers can use to target ads - that is basically an ad exchange. Instead of advertisers using AdWords (or whatever they currently use to advertise on NYT), they will use a custom built NYTWords to run their ads.

What I meant by subscription only is that their revenues won't be purely through subscription - ad revenue is still going to be a very significant part of their total revenues - they're not simply ditching it.