Eles parecem querer que as pessoas usem o Windows Live Mail, que é um download gratuito. Por que eles simplesmente não incluíram isso? Questões antitruste? Eu não sei. Eu não li nada oficial da Microsoft.
Isso é o que eles dizem sobre o recebimento de e-mail no Windows 7 em seu site.
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 other details.
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.
Se eu tivesse que adivinhar, eles querem que mais pessoas se inscrevam e usem o webmail para ajudar a gerar receita com publicidade.