ASP is not a straightforward program that can be picked up from scratch easily. However this is typical of a Microsoft application. The major reasons that large companies are running it instead of PHP include the following 3 important factors.
i)Microsoft products are all over the globe and it makes their site compatible with a significant number of other big businesses sites. This makes business to business transactions easier because everyone involved is running the same platforms and applications.
ii)Large companies already have their computers running Microsoft products and their employees are trained in the Microsoft program environment. This keeps training investments down to a minimum and keeps companies from investing in new equipment and software. They get to milk their current Microsoft product assets for all that they are worth.
iii)If a large company wants to take over another (an acquisition or merger) or is bought out themselves, the ability to easily integrate systems (databases, document processing, spread sheet and accounting applications) is invaluable and can make a company appear to be a much more attractive prospect to potential benefactors. Therefore keeping your business dressed up in MS clothing can have a certain appeal.
Independent Web developers as well as a growing number of small and medium sized businesses love PHP.
-It's easy to learn and the available support for it is through the roof. The Web has always been about individuals banding together to create resources for one another. PHP is loved by the Web community and you will find and abundance of tutorials, tools, Web sites and other online support ready and available to guide you from your Web sites conception to it's launch.
-More and more host servers are supporting PHP; chances are you can find a good free or cheap host for your site that will allow you to run a dynamic PHP site.
-ASP is supported by Microsoft servers only (unless you use a 3rd party utility that facilitates support); however, PHP is supported by many different "html" servers.
(Java Server Page) is an extension to the Java servlet technology pioneered by Sun.
Like ASP and PHP it provides a simple programming vehicle
for displaying dynamic Web content. JSP is the Sun/Java attempt to compete with Microsoft's ASP. JSP is not widely used however it has a small core of enthusiasts who are claiming it to be as powerful and dynamic as ASP. These patrons usually fail to even acknowledge the PHP genres existence (probably because PHP is far more popular than JSP).
ColdFusion is an application development tool created by Allaire Corporation. It is used for writing Web pages that interact with databases. ColdFusion Markup Language (CFML) makes use of HTML-like tags that are embedded in the Web pages. ColdFusion uses an engine (like PHP), which interfaces with a Windows-based Web server (obviously an attempt to make good use of the huge client base afforded to Microsoft).
However this would explain the reason it's not as popular as PHP amongst the anti Microsoft genre.