The newest online services use technologies previously used exclusively for "mobile" devices. For example, Twitter uses your location. It doesn't care whether you're on a desktop PC, a laptop or whatever, the location feature indicates the mobility of the user, not the device.
On the phone front, the usage distinction between mobile and landline phones is gone. One-quarter of all homes in America now have no landline phone. And even many that do have such phones, they're used only for telemarketing, DSL connectivity or some other unimportant use. From a usage model, people use "mobile" phones both as mobile phones, and also just as they did landline phones.
And finally, while rich people in rich countries often have the luxury of multiple devices -- desktop or laptop computers at home and work, iPads, smart phones and so on -- millions of people in the third world can afford just one computing device -- which tends to be a smart phone. To many third-world entrepreneurs, a smart phone isn't a phone; it's their company's data center.
Just like we dropped the word "transistor" when most radios had transistors, dropped the word "color" when most TVs had color and dropped the word "multimedia" when most PCs had multimedia, it's time to drop the word "mobile" because most computers, telephones and software are mobile.
If you still don't believe me, try to explain the purpose and function of a non-mobile computer or a non-mobile phone to a 20-year-old. For people who grew up with mobile tech, there is no other kind. Not really.
While the word "mobile" may still have some usefulness for Silicon Valley billionaires who need to offer subtly different versions of their apps for various devices, "mobile" is no longer needed for everyday speech to differentiate between movable tech, which is everything nowadays, and non-mobile, which practically doesn't exist anymore.