Sipping on halucinogens

I just read Paul Golding's take on Mobilisation and IMS (a little late!). He's a smart guy, so I was expecting some real concrete things I could get my hands around to justify why anyone is building IMS...
Well, I'm no wiser. Or perhaps I am. Paul says 3G is IMS, but then in his (long) article the only thing he mentions is SIP. He even interchanges IMS with SIP.
The formulas he uses tell the real story!

The Web = HTTP + Browser + HTML
SIP = SIP!
IMS=SIP + Some interfaces (e.g. [volume/quality based] billing)
3G=SIP + Presence
3G=IMS + Presence

That leads to the conclusion that IMS adds effectively nothing, from the customer perspective.
Given the cost of IMS and the proliferation of services that don't have or need billing interfaces (remember, we can still bill for access, presence and connection, without IMS!), what do we gain?
If IMS really adds nothing over SIP to 3G, then why on earth would anyone want to spend buckets of money implementing it!

SIP = IMS - something you don't need -> IMS = SIP

Implement SIP by all means, but move on to something more important...the customer.