Because I get a lot of email from people who have email names that I would like to modify to reflect my needs.
For example:
1. They use lowercase letters...for example: joe smith.
2. They didn't pick a name, so it just says joesmith@gmail.com
3. They use a nickname...for example: Donkey Balls
4. The name shows up differently depending on whether they send it from the web, from their email client, or a cell phone.
5. The same person has different email accounts that they send from and they all have different names attached. To me, that's one person, but they use different names.
6. They have corporate rules that make the email name something other than their name, but I know their full name.
7. They use the name Joe S., but I've known that person for years and know them as Joe Smith.
8. Maybe they use Joe Smith and I want to name them Donkey Balls.
9. They use the name Joseph, but I know them as Joe.
Why should it even matter? If I don't like it that way, there should be a way to reformat/change it. I find that people have many reasons for making their email name what it is, and I have my reasons for making it a name that I choose. I think that using an integrated system such as Mail and Address Book, there should be a way to choose what you want to do. That's why we have an address book...to personalize our contacts the way we want.
I would find this hard to explain to every person in my address book.