That's partly because it has the potential to reach unlimited numbers of people and distribution can continue long after the investment is made.
Unfortunately for the TV advertising industry, internet advertising is much cheaper than TV advertising too.
As a result, TV and other traditional forms of marketing are losing business to the vibrant, emerging digital marketing industry. I suspect this is why the TV advertising industry - represented by Thinkbox - is investing in advertising itself.
(Interestingly, Thinkbox is also investing in a digital marketing campaign, complete with social media (Twitter) and a blog.)
Thinkbox's mistake was to run a TV ad about a rescue dog called Harvey, who uses TV advertising to secure new owners:
But the video went viral, reaching far more people than the TV campaign ever could. Many internet users uploaded the video to YouTube, where it has been viewed millions of times (and counting):
One upload alone had received around 350,000 views by the date of this post, 22nd September 2010, only a few days after the video was first published.
The mainstream media also picked up the story. It was covered in one of the UK's leading newspapers the Guardian:
The Guardian story further promotes the video and comes complete with a valuable link to the Thinkbox website. This is another example of the importance of using SEO in traditional media campaigns. The Guardian story was shared via Twitter and Facebook many times, using the social media widget on the story's web page.
So the advert was a great success. But its success was viral, highlighting the fact that the product being advertised - TV advertising - is much less effective than internet advertising - which is also a far less costly medium.
No doubt the advert's viral success was helped by the TV campaign. But many other internet-only viral successes have shown that you don't need an expensive TV ad campaign in order to go viral.
Not long ago I blogged about the nonsensical claim, in the Chartered Institute of Marketing's magazine The Marketer, that viral advertising is "over" as an effective marketing medium.
Now Thinkbox is "the television marketing body for the main UK commercial broadcasters - Channel 4, Five, GMTV, ITV, Sky Media, Turner Media Innovations..." and others. Thinkbox has shown that digital marketing is much more effective than traditional marketing.