I was involved in the implementation of the preheat menus. Some people have custom heated beds which need quite some time to heat up. Thus the heat bed only option. The '1' options relate to multi-extruder systems where you have also a '2' (and so on) option and an 'all' option.
The case to heat up a nozzle and not the bed was not considered, that's true. The people involved into the extension didn't see a necessity for it. Personally, I still don't see any as I'm not a blue-tape-guy anymore (I was one before I built my own heated bed). But that's of course quite a biased opinion...
For heating up the nozzle only you will have to use the control menu. Of course you are free to extend the firmware even further (as it is open source!) and to issue a pull request for an additional preheat option. You have to know that changing something in the menus is quite a pain due to the fact that in the meantime there are 13 to 14 different languages the entries want to be covered for.
As I understand you have some issues with the adhesion on the glass bed. There is one thing you should never do on glass which you might be used to from blue tape: wipe it with alcohol, e.g. isopropanole. Actually you can wipe it with alcohol, but after that please make sure you clean it off with water and maybe a mild cleaning agent (I use dishwashing agent which includes lactide acid that leads to a very nice adhesion for PLA).
I hope this helps you to understand why the firmware is as it is and to enjoy successful printing directly on glass.