Generally pre-installed Windows OS comes packaged with PC and Laptops supplies to corporate houses and other buyers. This way MS Outlook by default becomes the Email client on users machines. Corporate executives  grown using MS Outlook for their emailing needs. They may not have  looked beyond Outlook. But that’s not the case with young fellows. The cost of training their employees to switchover to Gmail is another factor which weighs heavily on the minds of corporates.

Though relatively older generation still prefers using Outlook but the young have shunned Outlook in favour of Gmail. The Offline Gmail feature available with Google Gears have negated all the gains which Outlook was offering. But still corporates are loyal to Outlook in a big way.

Email isn’t just about the client software—it’s not just Gmail’s web interface vs. Outlook’s desktop software—it’s also about the servers supporting that client software, and that’s where Gmail truly shines.

Google charges its premium customers 25 GB with $50 per user/year.

Gmail offers:

• Security: Using https helps protect data from being hacked by third parties.
• Lots of applications to use – Google Docs, Gmail, Google Calendar, Google Groups, Google Video etc
• Can be used from anywhere. All your data resides in cloud.

MS Outlook offers:

• Better control over your data.
• Non-webhosted e-mail management.
• Cost: $150 (Approx.)

There is an interesting post on how people can judge you by looking at your email-id.

May also like to read:

Import your Microsoft Outlook Contacts into Gmail.