| Microsoft seems to be trying to hasten the demise of POP3 by no longer
| including any POP3 clients with Windows.

Not so much POP3 as "non-cloud computing".
Windows 8 tries to trick people into thinking they
need a Microsoft ID in order to use their computer.
As I understand it, that process also sets them
up with an outlook.com email address. The idea
is to keep people contained in Microsoft's version
of AOL.
It's all aimed at converting computer users to
service users who won't mind that they can't
control their computer, own their software, or
possess their data.

Government spooks, of course, are very happy
with that arrangement. It's creating an Orwellian
expectation that anyone who wants privacy must
be hiding something nefarious. Eric Schmidt of
Google, despite being known as a private person,
has been arrogant and/or naive enough to declare
as much. There's a very creepy clip of it he

https://www.youtube.com/watch?v=A6e7wfDHzew

What's really driving it for tech companies, though,
is just money. For years they were able to keep coming
out with new software and charge more for it. These
days most common software doesn't need to be paid for.
There are free alternatives. And the market has matured.
Products like MS Office and Adobe Photoshop haven't
really changed all that much since the 90s. Meanwhile,
those companies saw Steve Jobs creating locked down
devices, getting a 30% cut of software sales, and
making billions selling music through an online store.
And they saw Google become a mega-corporation by
switching their core product from search to spying, in
order to increase ad profit.

Microsoft wants a piece of that action. They've actually
been trying to get it ever since '98 when they came out
with Active Desktop, trying to convince people to
subscribe to "channels", which were intended to be
constant ad feeds from the likes of Disney that would be
mounted on the Desktop as embedded webpages.
(Remember the brief fad involving "thin clients" around
2000? Ever since PCs arrived there have been people
scheming to "rent you the car that you bought".)
Fortunately, Microsoft has so far failed to make
compelling spyware like Google. And they've mostly
failed to get people to buy restricted functionality, like
Apple's. Windows users are used to controlling the
hardware and software, so they've had to be herded
very slowly toward the services model. Thus the popular
dislike of the Metro giant button interface. People weren't
ready to trade their computer for a bunch of online
ad/service hybrids.