It's not the same. If I want Verizon to host my server, they have nothing to gain, but I do. So, yes, they should charge me. If instead they host a CDN server for a big content provider, they save money on routing content within their network.
That's not always the case though. Sometimes rack space is more valuable to ISPs than improving bandwidth efficiency via CDN co-location deals. It really depends how much space you've got to spare and who else wants it.
