The EU is equalizing laws and regulations. This is why in Germany you *can* sue Steam based on an EU regulation which is valid everywhere in the EU (however, Interpretations and enforcement may differ nationally). The courts ruled that steam has to make stuff bought resealable or (somehow) ownership transferable. It failed to do so.
The rest of the EULA is valid even if a part of it is void. But in this case the part is the entire section about purchases, ownership and transfer of it. So basically, 100% of what Steam actually is and does. This does not make the rest (non illegal) parts of the Eula invalid.
Also if Steam does not adhere to EU law, you can sue them in a EU court after you won the national court case. The EU courts are not kind to companies ignoring previous national rulings. So I am half hoping Steam is that stupid. Just for entertainment...
The VZBZ is our customer protection thingy so they are not sissies. If Steam thinks they can fight this out.. well if they enjoy paying lawyers?