I would very much like to know what this reason is, Spiral. I have never heard this before. I have been doing it for some time with no ill effects. And there are several reasons why I don't want to use a PHP extension.
Apparently you did not bother to read my first message posted above since I didn't say you couldn't have all your URLs end in .html as far as users and search engines are concerned, rather that you should *NOT* parse HTML files as PHP scripts!
You can still have web addresses end in .HTML to the outside world while internally within the server have the scripts properly setup as .PHP and my last post above tells you how to do just that!
Regarding your question, it substantially increases server loads (multiplied by the number of sites doing this) and has been known to cause substantial memory leak / corruption issues within Apache.
1) I have read that some people do not "trust" pages that don't end in HTML, and I certainly don't want that to be the case for a website where I'm trying to sell something!
Considering that more than 71% of the world wide web is directly PHP based (along with .php addresses), I highly doubt that assertion.
Irregardless, if you followed the instructions in my previous post, you could have .HTML urls if you so wished without violating setup protocols or possibly endangering your server stability.
Unfortunately, the inherent problems this causes aren't as widely known by average users and lessor experienced administrators as they should be as there hasn't been enough publicity mainly due likely to other concerns specifically dealing with security related matters if this were to get wider attention. More experienced administrators have all known about this issue for quite a while though and have been the base to try to routinely steer other users away from doing these things even if those users themselves do not fully understand the reasons behind doing things differently.
2) I have also read that Google prefers pages that end in HTML.
This I can tell you first hand, much more than you could possibly ever realize, that the above statement is absolutely and completely false!
In earlier versions of the web crawling system at Google, it was indeed programmed to read only .HTML and .HTM files specifically ignoring most of .ASP, .CGI, and .PHP files out there but that is no longer the case and there have been a great many revisions between that time and now including a period of slightly "misleading" rumors deliberately spread to trip up SEO people out there.
Many things have changed however I wouldn't dare suggest the logic might currently be reversed now or that PHP might have higher priority, I certainly wouldn't say that at all.
Unfortunately, I don't have references for either of these two "rumors", but I don't want to take any chances unless it's really necessary. The only alternative for me would be to rewrite the PHP sections of my pages in Perl, and SSI include them.
Again, it is very clear you didn't read my previous post!
If you did what I said, you wouldn't have to do anything to the files whatsoever other than rename the files and there would be absolutely
no file editing to do (except .htaccess)!
URLs to the outside world would continue to use .HTML or could actually connect by .PHP as well as it really wouldn't matter either way. The .HTML requests would be silently remapped to the .PHP files and by silent, I mean there is no way for the visitor to know that the URL has been remapped if you do it correctly.