QuoVadis' notability is established as it is 1) one of the leading certificate authorities in the world, 2) is licensed by several governments as an issuer of electronic credentials that provide specific legal benefits to their users (in fact one of the few CAs in the world to be licensed in multiple jurisdictions), 3) is a trusted third party, leading relying parties to wish to gather additional information about the company.
Wikipedia has good coverage of certificate authorities that specialise in SSL certificates. It is less thorough on CAs that focus on certificates for digital signatures. In particular, Wikipedia has slim coverage of the role of Qualified Certification Service Providers and Qualified Signatures (as defined in Directive 1999/93/EC). These are important concepts in e-business, particularly impacting e-government initiatives and e-invoicing in Europe.