>there are plenty of other things to do on a computer while you wait through the ad.
Yea, for example you can buy the advertised product with a few clicks. If you are quick enough then you can finish the buying even before the video ad finishes (sure it's not the most realistic scenario but it's possible). Or with a quick search you can learn more about the product to check how honest is the ad. TV ads cannot compete with this efficiency. The only thing TV ads can do better is reaching bigger and the less tech interested audience.