Why do Ancestry.com and eHarmony.com use TV?

Is anyone else tired of seeing ads on TV for sites like eHarmony.com, or Ancestry.com, or really any site that requires a subscription to get value?  I understand that it's part of their growth strategy, but think of how much cheaper the service could be (or free) if they weren't buying 30 second spots in prime time. The truly useful, and truly desired sites don't need any help getting users.  Word of mouth through social sharing does the job.