To be honest about it Linux Mint development relies solely on donations, whatever income is generated by Mint's customized search page in Firefox and the ads on their site and forums--that's it. And although I tend to despise most of ads placed on websites these days I can't really fault Mint for having to use them considering the high quality of their releases. As far as mailing lists are concerned, the current number of (one paid and only 3 or 4 dedicated volunteers) developers really doesn't warrant it--yet. I wouldn't be surprised to see a mailing list popping up in the relatively near future though.