I agree with you in principal, but think that your comment (and the MANY like it) actually miss the point of this new feature.
This labs feature is NOT to replace POP or IMAP. It is for people who want to use the WEBMAIL interface even when they have no internet connection.
The reasons for this could be many: perhaps they have no POP/IMAP client installed, do not know how to setup a local client, or simply prefer the Gmail interface. I don't know why - but I do know that we all know - and that the Google developers know - that IMAP and POP have been available for a long time!