Well.. I'll give you that one. Except that Apple doesn't just double click "exe"'s either... however the underlying point still stands that they are accustomed to double clicking the package of their OS's preference.

OTOH: Lets explore this a minute,
the iPhone you can not just double click a package file, because there is no package file.. you have to install through the iStore (or whatever it is).

Oh Android.. you can click a package file, after setting a setting in the settings panel to not protect you from being an idiot.

A Jailbroken iPhone will give you the ability to click on a file and install.. after you've voided your warranty.

A rooted Android is a PITA, and you still have to set that setting that you're ok with being stupid.

However, both Android and iPhone apps are limited in and of themselves in their access to the systems unless rooted, and both try to protect users from themselves in some way. Apple more so than google, but both the same. so the chances of installing a horrible app that crashes the device is less on these more controlled systems.

In Maemo, otoh, all of the application management is done as root with, or without rootsh installed. Which means that all apps have full control to everything on your phone. Something never before done on any other phone out there. It's an entirely new beast. Just a checkbox saying "Ok I'm dumb." isn't quite enough in this ecosystem. And even still, they aren't preventing you from installing the app - they are just making sure you really want to be dumb in order to do it.