With the addition of Yahoo (NSDQ: YHOO) to the CBS Audience Networks confirmed today, CBS Interactive (NYSE: CBS) can claim 92 percent unduplicated reach in the U.S.—meaning the number of people who can access CBS video is higher. But that doesn’t guarantee that they will watch. Talking to CBS Interactive president Quincy Smith this morning, a favorite Dorothy Parker-ism came to mind: “You can lead a horticulture, but you can’t make her think.” CBS can’t make people watch or, as Smith puts it, “You can’t jam anything down people’s throats ... it’s up to the content now.”

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The hope, of course, for Smith and others in this situation—think Hulu, for instance, which launched with 90 percent penetration—is that making it available to more people increases the number of actual viewers. Repeat visits matter as well. But getting people in and getting them to come back requires content they want to see. Walt Mossberg raved about Hulu’s interface at D6 last week but he also mentioned that back at launch, for him, the content was lacking. Smith is counting on “great new events and shows coming up.”

As for Yahoo, the CBS Audience Network gives it three of the top four broadcast networks (it was a charter member of the Hulu Nation when it was still NewSite), in addition to more than a dozen cable nets. Perhaps the most surprising element about this is that it’s just happening now despite long-standing agreements with Yahoo News for “60 Minutes” and local news from the CBS O&Os. Smith told me the discussions stretch back 18 months and that getting it done primarily was about focus on both parts.