There is more under the hood Gilles; it’s not the demo portal and the site does not need every possible feature :-)
First, implementation allows rendering of attributes as single value text or multi value comma separated text, multiline text (one attribute value per row) etc. and yes, as combo box too. Every attribute value can have assigned its own price increment (surcharge) and the total price is computed on the page dynamically. It accepts even every currently implemented token as value, e.g. [DIMENSIONS], [WEIGHT] etc.
Second, the rendering possibilities are easily expandable.
Finally, everything you are writing about in your previous post is with this implementation possible. For example usual T-shirts with different colors, sizes and of course with different prices.
Gilles, you are wrong with your idea of modified Product Edit form. This implementation uses its own admin page (plugged admin tab) where one can define his own attribute names and attribute values pairs. That name/value pairs can be freely assigned to one or many existing products. This is completely independent from the existing official store product implementation. No new fields in Products table etc. It uses its own table set. Generally speaking the features of official Store module are left intact.