I think a key difference is that Android for most people is a mostly-closed ecosystem. Most people can only install that which has been added to the small selection of app stores and the OS configuration is at least partially locked down. There have been an uptick in malware targeting Android [1] just one recent example but people are not installing as many random applications and vulnerable frameworks such as Wordpress or random apps that lack GPG verification, curl | sudo bash. This puts the onus on Google and wireless vendors to manage the security of these devices and most applications.
If some day there is a truly open Linux distro on fully unlocked-by-default phones that come with root access enabled and said phones are adopted by the masses and people can tweak the OS however they wish without using debugging tools or installing custom images then I think the phones will almost be on equal footing to Linux desktops, gaming and graphics power aside. They key part being adopted by the masses.
Even Android is not a majority market share [2] so people would have to target apps that Android, Apple and others share.
Android by itself has 50% more devices than Windows.