Since when has a stock standard BGP-peering arrangement been worthy of headlined marketing space on this website?

Anyone with an ASN and some IP address space can join an IX and set up bilateral peering arrangements and/or use the route servers. In the case of Microsoft they do not announce on the route servers so all of their peering arrangements are bilaterals. Any IX participant can fill out their form and apply for a bilateral. While I don't have specific numbers I would expect most of the IX participants - especially ISP's - are peered with Microsoft.