It's not about the security of XP users; it's about their connectivity.
Connectivity and security need to be considered the same thing on the modern Internet. XP is no longer supported, and that leaves it in a pretty dangerous position. A unpatched computer isn't just a risk to the user of that computer, it becomes a risk to everybody on the net as it tries to spread its latest infection.
That is true. But it the user's main concern is the legs of network from their location out of a local untrusted network (such as communal wireless) or country, that is definitely better than nothing.
> XP still has 19% market share
I don't worry about the security of XP+IE users any more. Anyone still there has chosen against good advice to remain insecure. It is their choice when there are other options available (both browsers that support modern standards on XP, and alternate OSs), it is their choice to have the certificate warning and more iffy security when they hit a site that needs SNI.