Who cares about CO2?

I do. Among other things.

Airplanes produce less CO2 per passenger mile than buses.

Airplanes are used to travel much further distances than buses. And by reducing the marginal cost of that travel, greatly increase the total amount traveled. So while a typical daily motor vehicle trip is on the order of 35 miles (based on average annual miles driven in the US), air flights are typically 10-100 times that (300-3000) or more. And with take-off and altitude gain, short-haul flights are relatively less efficient than long-haul. The per-trip CO2 emissions are thus vastly higher -- you're dividing by 2-4, but multiplying by 10-100.

Additionally, many of the modes listed on your reference can substitute electricity (which can be generated from non-fossil sources). Heavier-than-air travel pretty much doesn't exist without fossil fuels: liquid hydrocarbons are simply too dense, cheap, and versatile a fuel and energy carrier. The maths on biofuels simply don't work out, except at very low fractions of existing fossil fuel use. Substituting 10% of present oil consumption biofuels might be possible), but with an effective cost of $600/barrel or more, and that 10% would have to supply portable, emergency, and defense, as well as commercial aviation needs. I see lighter-than-air craft as more viable in a not too distant future.

And if you do want to talk about CO2, how about CO2 per GDP?

That works out roughly to the amount of fossil fuels used per unit GDP, though it varies based on fuel source (which I don't factor in). I used Wolfram-Alpha to look up GDP per quadrillion BTUs a couple months back:

For China & India, it's about $60b/quad.

http://www.wolframalpha.com/input/?i=china+GDP+%2F+%28total+...

http://www.wolframalpha.com/input/?i=india+GDP+%2F+%28total+...

And for comparison, the United States -- we use far more energy, but use it far more efficiently as well at $150b/quad:
http://www.wolframalpha.com/input/?i=United+States++GDP+%2F+...
But nothing like the Swiss at just a hair under $400b/quad:
http://www.wolframalpha.com/input/?i=Switzerland+GDP+%2F+%28...

Italy shows in at ~$275b, Germany ~200 (plot's a bit wonky), UK ~$250b/quad, Spain ~$240b/quad, Japan ~$250b/quad, Russia ~$40b/quad.

Incidentally, growth in GDP and energy use for China & India:

http://www.wolframalpha.com/input/?i=china+total+primary+ene...

http://www.wolframalpha.com/input/?i=india+total+primary+ene...

After all we can't keep the entire world in poverty in order to reduce CO2.

I see no real choice in the matter. GDP's going to get tanked one way or othe other (climate change, peak oil, peak everything). We're on an unsustainable path. Not cutting carbon emissions is going to be rather markedly worse than cutting them, in the long run (though next quarter's profits will take a hit in the latter case but not former). And we're going to have to learn to get by on vastly fewer fossil fuels as well.

As I've said elsewhere, the only reason China has low numbers is because of the human misery of their poor population.

Given their present energy mix, yes. However if they were to pursue renewables to a maximum extent, you might be proven wrong (I've got some doubts on the feasibility of this as well, but given other alternatives, it's really the only option we've got).