The spell checking is often very useful when editing code, and underlining URL’s seems pretty harmless. Those URL’s open if you double click them - which can be extremely useful even within code - and the underlining alerts you to the fact that this is possible. I find it handy to put URL’s inside C comments, and sometimes code opens a URL, and it is convenient to check the URL by double clicking. Why would you ever not want the option to open a URL that is embedded in your text? Without the spell checker, I would never find odd spelling errors buried in rarely used error messages!
Defaulting features to OFF has the disadvantage that busy people probably never discover they exist!
Maybe it would help if users could vote for or against proposed changes - my bet is that a LOT of people are very happy with the vast majority of NP++features!