Personally, I believe a business logic layer is a good thing, almost to the point of a "always-must-have". I suppose there can be some arguement made that depending upon size and scope, every project may not need one. But having been on enough projects that have grown beyond their original scope and intent, I believe it can't hurt. Especially if a project manager describes it with phrases like "its just a. . ." or "its only a . . ." or "its a really simple thing". But I digress.
I can't see a compelling reason not to use them for web apps. Besides, today's web app can turn into tomorrow's smart client app. Having clear lines between the presentation, business and data layers makes those types of transistions easier.
A business logic layer also helps with testing. You can test your business processes seperate from your UI or database.
My problem with the tutorial you referenced is that to me, it seems more like a DAL than a BLL. Maybe its because it works with typed datasets and datatables. Maybe its because it takes in alot of individual parameters. I don't know. Its a easy way to whip up one via Visual Studio and interact with the rest of the built-in tools.
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