Thank you for your questions, and welcome to the ExpressionEngine forums.
First, I would suggest a few resources to come up to speed on ExpressionEngine. The very being The Big Picture which gives you a short and sweet look at ExpressionEngine.
Then I would check out the getting started section of the User Guide. It’s a great way to understand how ExpressionEngine works. This video is also a great way to get your feet wet.
With some of background on ExpressionEngine under your belt you will be better prepared to understand why ExpressionEngine is more than a CMS and how it’s flexibility is far superior than say WordPress.
I would say that your websites would be built quicker in ExpressionEngine, but the real benefit is that it’s does not assume anything about your data or force you into any workflow. In other words “ExpressionEngine doesn’t force you to work a certain way or impose limitations on your site design, structure, or content. Its flexibility allows you to build a website that not only fulfills your needs and creative vision today, but will grow and scale as your business needs change in the future.”
Wordpress is free, so cheaper as far as the up front cost to purchase the software. But I believe that ExpressionEngine is cheaper in the long run because unlike the software you have named, you can do a lot more and do it faster. You make up hours and hours in Development time with ExpressionEngine. ExpressionEngine makes DRY very easy!
I used to create sites in WordPress, and that’s about it. If I wanted something that was not a blog with entries and posts, then I had to hack things up. ExpressionEngine allows you to build websites, but that’s not all. ExpressionEngine really does not care about your content, you can actually Develop! Want to output web pages, cool. Output RSS, or CSS, then awesome. You can output the content as PDF’s if you want. Not forcing you into a blog format but giving you “web software” is one of the areas where ExpressionEngine really shines.
I am not aware of how the cart Add-Ons for the other products work, so I can not compare. But I know that Magento will work with ExpressionEngine and that our other Add-Ons like Brillian Retail work very well for folks.
I would also point out that our support is just plain awesome and that our community and developer community is rather large. Add-Ons are vast and so are tutorials, firms that use ExpressionEngine, and Developers that make a living writing Add-Ons for ExpressionEngine.
You have not asked too many questions at all!
If you need ANYTHING, please just let me know.