mailto: links are relics of a past era. As seen in many usability studies, ANYTHING that looks like a link will be treated as one, even if it is a hyperlinked email address. Nowadays, most users have web-based email clients, and, as you stated, mailto: opens the desktop email system. I dislike even the
"Get help from our friendly support team: [email protected]"
example because there still is a chance that a user might accidentally click the mailto link while highlighting the address. This severely disrupts the user experience, which results users leaving the site frustrated.
Simply emphasizing the email address is a better way of indicating an important address.
A better example is this:
"Get help from our friendly support team: [email protected]"
I also believe that the majority of users are experienced with copying and pasting sections of text on the web. Therefore, if you want to ensure you please everybody, simply allow the users to copy and paste the email address into the email client of their choice.
By eliminating the mailto: links, you can ensure that they do not appear in unexpected locations. Taking an extra 10 seconds it takes to copy and paste an email address is not going to deter many users; however, placing a link that eats up 30 seconds by bringing up an unwanted program is more of a deal-breaker.