Is that necessary to have multiple web hosting (let's say, two) for a website?

yes

There are many reasons to have multiple domains. One of the most common is simply because the person with the web hosting account has multiple projects on the web under different domain names. They choose to host them all off their web hosting account, which allows them to more easily manage all the web sites they have up.

By utilizing one primary hosting account the user can see statistics and manage the mail server for all of the domains from one control panel and having email redirected from one domain to another is easier when it is all handled internally.

Another incredibly common reason to have multiple domain names registered is to make sure that the person who owns a .com name also owns the .net and other internet extensions. It can be very difficult to do business should a business own and use the .com but a competitor or spammer gets hold of the .net extension.

Hi,
I think no because I have used Mywindowshosting.com for my business since 1 year and still I have no complain about this and I am getting more traffic on my website. So the main point is to choose the best hosting service which satisfies you completely.
Thanks a lot..