You still have to write an absurd amount of spaghetti code around testing GL extensions that are available. Especially when you consider the Intel IGPUs from the last 5 years - the first gen is only 2.1, second gen 3.1, and Ivy Bridge and above is 4.3. But besides those the Nvidia / AMD parts have supported 3.3 and above since 2006.
Of course, if you are targeting Windows XP... you got to think back a lot further than that. In some ways theres some elegance in how you can write GLES2 shader code and have it run everywhere, including on mobile, and just check extensions for everything else you use.