Moving from offline only to online only -- is there any reason not to?

Life Magazine is printing its last issue this month. Today we learn Child magazine is moving online-only this summer. Why? It's easy. Significantly lower expenses and the promise of greater revenue. MySpace reportedly is earning $30 million in revenue per month.

Wired print magazine this month has 57% ads. That means for every page (or half page) of content, there is a full-page ad. Is this what magazines need to do to survive? If so, I get the idea of moving online-only. 

On the surface, it looks like a great opportunity. I am wondering though, will the Internet become clogged with these new online-only magazines? We have to decide where we spend our time offline, which magazine(s) to purchase and subscribe to. And now we will need to determine which online magazines we will read and RSS to. Will these online-only offerings be able to survive as more noise comes into play?

So you are probably asking what does this have to do with a Web startup? Simple. These magazines MUST differentiate themselves online. Even more than they had to do with the print mag. You need to do the same thing with your web app. On American Idol (and I am sure all the world idol competitions), the judges say over and over, "if you want to win, you have to make it your own (dog)."

Think about this as a starting point. You are in an elevator with a major VC. You have 45 floors to ride. What will you say to this VC about your startup. How will you explain why it's better than x or y player in the current market. If you can't do this, then don't launch until you can.