Why are to do lists so important?

I don't feel the 'Todo list' project is meant to show that you have any specific skill. They are simply a good learning tool because they provide a simple and complete implementation that could easily be extended. Once you have a ToDo list working, you could use these skills to create your own simple project, and build from it.

A Todo list has:

• A managed collection, like a list.
• State (checked/unchecked)
• Some kind of data layer
• Some kind of presentation layer

Together these features scale well, and can be extended to support things far more complex and impressive. For example - You could take the ToDo list, and turn it into a shopping list. You obviously have implemented some kind of Collection to store your list items, so you could use 2 collections; one to store what is on your shopping list, and one to store things you can add to your shopping list (Pre filled with apples and pears and stuff...). You could then extend this to 3 collections, and have multiple shopping lists, so you can show 'shopping list histories' and maybe then extend that with some cooler features leveraging the data, like predicting what a user will add to a new list based on what they have bought before...

As far as portfolio assets go, a simple Todo list isn't impressive nor of value in my opinion, but you could make it so by using your creativity to extend it, and make it something awesome! If in doubt, look at other people's portfolios and find some you feel are impressive, and see what features their work exhibits that you could try to implement your own way in your own projects. Ultimately, only you should decide what you exhibit on your portfolio, as it is a demonstration of your skills and work - not someone else.