Self-driving vehicles will probably replace the need for most of these employees, however.

Shit, with retarded patent system in US someone is already patenting this as you read my post.

I agree that the last-mile driver will stick around for a bit longer, but their number is relatively small.

For example: UPS owns 100k vehicles, worldwide[1].

In comparison, over 3 million people are employed by the transportation industry in the US alone[2].

[1] http://www.ups.com/content/us/en/about/facts/worldwide.html

[2] http://www.bls.gov/emp/ep_table_201.htm

What am I missing?

Although I suspect a compressed air tank with enough capacity would be way too heavy for a drone to carry.

The power to weight ratio is the key issue. Also -- noise could be an issue too -- want to have quiet deliveries.

I'm thinking parcel cannon + small airbag bumpers and maybe a little parachute to slow decent at exactly the right time :)