An eCommerce website is a website which allows your business to sell products and services to their online audience.
Nothing to download. Nothing to install
No more updates
Lends itself better to a recurring pricing model
Downloadable apps are associated with one-off payments. You buy it, you own it.
Web apps seem to lend themselves better to the more profitable recurring payment structure.
Access to analytics
From a business point of view, being able to see first hand how your users interact with your product can be a huge advantage. It can help you cut any usability issues and reassess features that nobody is engaging with.
Less expensive to develop
A website provides an instant visual presentation, can be found through search engines, is always available, is interactive, can target each visitor specifically, is easily updated, saves on printing and mailing costs, improves customer relations.