I'm typically a big fan of TechCrunch and it is one of my two must-read blogs that I read every chance I get. The other is DownloadSquad but I have to say that this blog entry definitely missed the mark on the topic. I'm definitely a big fan of trying out different webmail services that are free just to compare them and have had many an email account purged over time but personally I don't have a problem with that in principal or in practice.
In principal, these companies make money through advertising and an inactive user is not any different from a deadbeat customer. Yes, while storage is indeed much cheaper than it was a few years ago. Cheap is still not the same as free. Any business has to be financially prudent as going out of business does no one any good. I think sometimes it's forgotten that the primary purpose of most companies is to make money. Usually by providing users with something useful or convenient that will by in some means generate money but it's still primarily to make money.
In practice, if I'm not using an email account at least once a month, it's really not that important to me anyway. I've got multiple accounts sometimes with the same provider but I access them at least once a month. I think most companies have pretty generous terms in terms of the activity requirement. Another thing to note too is that most of the major providers give you a means to back up your email via IMAP, POP or HTTP. There's no real excuse to having your email account not being backed up.
In general, I think this blog post was a bit off and looking at the general comments, it looks like most of the commenters agree with the sentiment.