How many customer do I lose if my webpage is not accessible from www subdomain. Can anyone who has webpage analytics with large number of visitors provide me statistic how many users use www.domain.com and how many only domain.com? Thanks a lot
Not too many. Most modern browsers (chrome, ie10, safari) will do a dns correction for you. So if you type in www.yoursite.com but a www record does not exist, then they will try their best to figure out the correct place to send your visitor. IN browsers that have search/address bar like chrome, the worst case is that google or whatever search is set as default will come up with results that put you at top.
Now, there is no reason to do this. In almost all hosting scenarios you will be able to redirect www to non www or vice versa. If you are on IIS (windows) or Apache or Nginx all three support rewrite rules that can set this up for you almost instantly. These are done with 301 redirects, which tell the browser that the site has been permanently moved.
If you tell us what type of server you are on, we can probably help you out. In some scenarios (windows azure, heroku, and EC2 without a static ip), you will have to get a little more creative with dns to resolve this issue. This is because they do not allow redirecting of naked domains, and dont always offer a static ip address. In those scenarios dns redirects are used where the dns records are set to mirror or auto update.