See here for a recent extension of the discussion:

http://groups.google.com/group/comp.lang.python/browse_frm/thread/7e9327a896c242e7/

For what it's worth, bypassing the dogma, methods like index and count on tuples are not exactly compelling in many situations (as I've pointed out before), but such issues should hardly derail the core development effort. If people consider such methods useful and if it diminishes perceived inelegance without method proliferation, just add them: people will be less frustrated and feel listened to; the language will become more regular.

The only downside is any additional memory consumption. Objections related to what such methods mean, or what a tuple itself should be taken to mean, risk venturing into dogma and a consequent time-consuming discussion which takes 100 times the effort of just getting stuff done. Just look at the referenced thread (and the others of recent times) for example material.