They seem to want people to use Windows Live Mail which is a free download. Why didn't they just include it? Antitrust issues? I don't know. I haven't read anything official from Microsoft.
This is what they say about getting e-mail in Windows 7 from their website.
An e‑mail program or web-based e‑mail
service. You can download or purchase
e‑mail programs from Microsoft or
another provider. E‑mail programs
often have more features and are
faster to search than most web-based
e‑mail services. Before you set up an
e‑mail program, you'll need to get
some information from your ISP:
usually your e‑mail address, password,
the names of your incoming and
outgoing e‑mail servers, and certain
If you don't want to download or
purchase an e‑mail program, you can
instead sign up with a free web-based
e‑mail service, such as Gmail, Windows
Live Hotmail, or Yahoo! Mail. These
services allow you to check your
e‑mail with a web browser from any
computer connected to the
Internet—even a computer that belongs
to someone else or is in a public
location such as a library.
If I had to guess, they want more people signing up for and using webmail to help drive some advertising revenue.