As the article notes, if you were online in Germany in the mid-90's, chances are you were either at a university or you used one of three ISPs: T-Online, AOL, or CompuServe.
Even our company's Internet connectivity at the time was via a dial-up CompuServe connection and our email via CompuServe's MHS service. (I was—IIRC—MHS:PNE@DATREV at the time, or INTERNET:PNE@DATREV.MHS.COMPUSERVE.COM.)
As of 31 July, people won't be able to connect to the Internet via CompuServe Germany (a service of AOL Europe Services SARL in Luxembourg) any more—and their @compuserve.de addresses will stop working, too.
Sic transit gloria mundi. Sure, there were people who cursed at Compu$erve (as some called it), but it was an important way to access lots of content (including the Internet, though they also had a lot of content in their own little walled garden back then, too) back in this days.
So it's kind of significant when one of those oldbies closes their doors, even if they were probably only a minority ISP in the last years.