I don't see what the big deal is...
You've always been able to use iChat to send texts to someone's iPhone (or any mobile phone, for that matter). Simply use "1+phone_number@aol.com" as the recipient address, and you can chat back and forth between mobile and desktop all day. Granted, it's not full iOS/iChat integration, and standard mobile messaging rates apply, but the capability is there.
I agree with those who say Internet-based (non SMS) texting, media sharing, and Facetime video should all be collapsed to one app that works with the desktop version of iChat, but Apple seem to be taking their sweet time getting there. I think it's just one of those cases where they think there is a sales-driven reason not to combine them, and they don't feel they owe anyone an explanation for the awkward disconnect.