You are so right. Seriosly, I would never, NEVER code on my Android phone. And why should I? It is a small device with a small display and small keys - I would not like to search for a specific line of code in a 2000 LOC document.. seriously.
I am a CS guy, so I have my laptop around me most of the time when I feel like I need to code something. That's far enough I think.
When I was a kid, I sometimes went to toy shops during school lunch hour and coded BASIC on a toy computer with one LCD row of text (couldn't afford a home computer).
Why would one want to code on an Android device? Not everyone uses laptops all the time. Laptops need to be lugged around (even though mine's a Toshiba Portege, and is lighter than most at ~1.2kg, I seldom bring it anywhere), opened up, resumed (takes a second or two), balanced on a knee (so you need to be sitting), etc. Hard to do when you're e.g. waiting in a queue, walking in the countryside, lying in bed (without rearranging pillows, sitting up, lighting up the room from the screen, fans and light disturbing your significant other, etc.)
And then there's the idea that you're writing programs for your device without the need for a deployment stage. You're running them right there on the device. No need to faff about with cables, or build / deploy steps.
As to lines of code, in a structure-oriented editor, I think that would not be relevant. I would imagine program navigation to be spatial with drill-down, up and out; all identifiers are hotlinks to their definitions; MRU lists and the same Patricia trie technique, or incremental search, for more random access, etc.
