Why, on my iPhone, do I have:
1. An email app (which required a major update to unite mail boxes)
2. A "messages" app (which abstracts out two different message systems)
3. A phone app
4. A contacts app
5. Twitter
6. Facebook
7. Skype
What I want to do is (a) send messages to people (I don't care how), (b) check messages I've received (from anyone, using any method), (c) manage my messages (both incoming and outgoing), and -- as the writer of the article points out -- (d) manage my attachments.
On the iPhone (which is by no means the worst case) I might end up doing something stupid like looking up a contact, phone them, get sent to voicemail. Go back to the contact. Use a slightly different path to send an SMS. Discover it doesn't get sent. Switch to mail, and send a message.
Meanwhile the recipient gets a missed call, an empty voicemail, eventually gets the SMS, and then receives an email -- in three different apps on their iPhone.
Tiny incremental improvements to email will only nibble at the edges of the larger problem. Let me communicate with a unified UI and unified contacts.