Let me start out by saying I do not totally agree with your assessment so am not sure if the following helps or not.
Here is my two cents:
Zimbra hosted or on your own is one of the best products. It provides much of the functions of both Exchange and Google Apps. I use Zimbra for a home/family on an old dell server. Yahoo, the company, is making yearly profits, its investors are taking a bath http://yhoo.client.shareholder.com/sec.cfm?DocType=Proxy.
I use Exchange at work and have not used anything else since 2000. I am not sure about what you mean "hard for others" using imap or pop any good mail program can hook up with exchange. I have used OWA with Opera and Chrome without ant issue and Firefox (which provides a different look and feel). Exchange has so many third party apps that you can make it do just about anything including project management, NPO get a great deal on Exchange here at Techsoup. If you are in a Linux environment use http://www.bynari.net/ with or without exchange. If you use SBS then you will get lots of extra functions. The intergretion with Office Live reduces the document management issue.
Google apps is well tested. Many colleges and some businesses use the education edition, without many issues. http://www.google.com/a/help/intl/en/edu/index.html
Hosted Exchange for 60 people is fairly expensive ($600 per month) so if I was looking for hosted use Zimbra ( at $250 per month for a whole server) or google apps education edition (free).
For pure functions Exchange gives you the most number, deepest, and most mature. It also does sharing information the best.
Zimbra Server is the great, cheap, and allows a Exchange like experience.
Google Apps allow the person to take it with them if they were to leave the organization (good and bad here), the apps are good but they do not connect as seamlessly as with Exchange or Zimbra, IMO.