Actually people are making a wise financial decision when they do this -- email service is something that you cannot stop or easily change overnight; coffee is something you can. If and when they are in a serious financial crunch (and even the moderately rich worry about this happening), they can stop spending the $5 on the latte, but if they used a paid email service they cannot stop spending the money on the email service because it is usually very critical to a lot of their future. With free and relatively good email services like YMail, GMail and Outlook, it doesn't make sound financial sense to spend money on a paid service that is critical to your daily life that you cannot cut it off when you are in a financially bad situation. Also the same people would go for free coffee if someone did offer free coffee daily at the same quality level as their favorite latte shop.
If you've told everyone your email address is myname@somefreeprovider.com, it's almost impossible for you to move for whatever reason. The switching costs are actually very high. If it's myname@mydomain.com, you can move your email provider at will, and you're unlikely to ever be forced to pay more than $10 per year, which is pocket money for most folk.
