Well, from an author’s perspective web-based IF is a method to reach a larger audience. This isn’t only my conviction. Many people view it the same way. Especially for unknown authors or non-established game developers it is a good method to present their work to a bigger cloud of people. Other methods of delivery (as you call it) may exist to accomplish the same goal. But I can’t think of any.
I could imagine that with the release of internet-enabled portable devices, such as iPhone and iPad, there are people in this world who have permanent 24-hour online access, for business, job-related or other reasons. But I agree, it hasn’t become the norm yet.
It’s a legitimate point of yours. But I think you should also point out why some people find it impractical to play in a web browser. What are the barriers for those people?