Why is Evolution the default mail/calendar package that comes with Ubuntu?

Why not Thunderbird + Lightning?

Are there any features in Evolution that are not available in Thunderbird + Lightning? 

Can I use the Evolution database via a Samba network share, on a Windows XP or 7 client, just like I can do with Thunderbird?

What happens if I uninstall Evolution from my 10.04 system? Will I lose any integrated functionality built into the system?