Probably the biggest part of comics is the actual ownership...watching your collection grow and flipping back through your long boxes, so I don't think e-comics will or ever should replace the real thing.
However, there's a lot of titles that suffer and die out because they've never caught on.
Dave Chapelle realized his show wasn't catching on because it hadn't found it's audience so he made early episodes available for free download himself. Look what happened there.
If Squadron Supreme or Blue Beetle is on the verge of cancellation, why shouldn't Marvel or DC make issues available on their websites for free? After all, the issues are already a loss and if you can grab new readers you might be able to push the series a little further.
The anti-arguement is that people may stop buying new issues and wait for the download. But does that prevent people from buying new release to wait for the trade paperback? I know I myself have trades of a lot of storylines I already owned, just for the sake of preserving the condition of often read issues. In the case of Watchmen I have the originals, a trade to lend out, and the hardcover.
The comics industry has it's ups and downs, and in the downs I think the big guns should pull whatever they can to keep the machine running.