Why does SkyDrive require I login with my Hotmail account?

In this excerpt from
Answercast #73, I look at some confusion about features, such as Hotmail and SkyDrive, that are offered in every Microsoft account.

SkyDrive and Hotmail

Well, I'll put it this way. In order to access SkyDrive, you must log in with
your Microsoft account. That's all that's required.

As it turns out, your Hotmail account is your Microsoft account. In
fact, your Microsoft account often looks like, I will say, a Hotmail
account.

Use another email

You can set up another Microsoft account using a different email address
that is not a Hotmail account, and you can access SkyDrive using that. But it
does require setting up a separate account that does not use your Hotmail
address as your login ID.

You need a Microsoft account

The bottom line is that you need a Microsoft account to access this
technology.

My recommendation is use the one you've got. Moving is probably going to be
much more effort than it's worth. If you're not using Hotmail, you know what?
That's OK. Don't go there. Just use SkyDrive. Use it to whatever degree you want
to; ignore the Hotmail.com email address completely and you'll be fine. There's
absolutely nothing wrong with doing that and that is in fact what I recommend
you do.

(Transcript lightly edited for readability.)