Preventing a web page from changing requires continuous significant effort. Changing a paper contract requires significant effort, unless you just, you know, lose it, or drop it in the gutter, or something.
Yes, if what the parties are looking at to sign is the printed web page. But we're commenting on an article about signing contracts via email. If they each print the web page separately, they may print out different versions of it. A more effective measure would be to send the contract in the email in some kind of self-contained format such as PDF or plain text.
