However if the primary purpose of the site is to SELL something, then entirly different factors come into play. I'm not sure what you mean by this.
Surely if the site is there to sell someting external (a physical item, a real-world service etc.), then the job of the website should be to make information about that product or service as easy to find and use as possible. If the site is there to sell something directly (access to a "private area", or whatever) than it still has the job of making as much information as possible available to prospective purchasers about what they will get in
exchange for their cash.
In neither of the above cases does making anything hard to find, slow to download, or dependent on particular browsers, plugins or operating systems aid the cause.
Please explain a bit more about how difficult or irritating sites can aid selling stuff.