It doesn't work everywhere, it's not expected to work robustly anywhere, even if your server supports it not all clients will and there's just no need to do it. No matter how many out of date RFCs you quote. This hasn't changed in the past 10 years!
% dig +noall +comments +stats pzxc.com.
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 14316
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; Query time: 161 msec
;; SERVER: 75.75.75.75#53(75.75.75.75)
;; WHEN: Sat May 28 02:38:43 2011
;; MSG SIZE rcvd: 26
% dig +noall +comments +stats joyeur.com.
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 57255
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; Query time: 133 msec
;; SERVER: 75.75.75.75#53(75.75.75.75)
;; WHEN: Sat May 28 02:40:38 2011
;; MSG SIZE rcvd: 28
So, yeah, using CNAMEs on your domains works great, except for all those times it doesn't work at all, like with the largest residential ISP in the United States.