You're adding weight to actions and ignoring weight on other actions. "Go to app sore, find app, click 'buy', enter password" isn't really any simpler than "Go to URL, click '+', click 'add to home screen'".
Neither is "instant", though the App store process is streamlined to a specific purpose.
The difference is that you can visit a website without adding it to your Springboard. You can't try an app, however, without adding it to your Springboard. I'm weighing requirements vs. options.
Neither is "instant", though the App store process is streamlined to a specific purpose.