Complete rubbish, they have no such obligation at all!
The only legal obligation that have is that they must not mislead as to future content which can be reasonably expected to be an inducement to purchase: lack of information is NOT misleading, advertising must be ACCURATE, completeness doesn't come into it.
Providing limited, or non-existent information is clearly not 'illegal', someone is free to 'pre-purchase' if they trust the seller, or not as the case may be, they will only have legal recourse if any statement made prior to purchase proves to be false later on.
Pff... now I'll have to look it up. There you go:
EU Distance Selling Directive, Article 4:
Prior information
1. In good time prior to the conclusion of any distance contract, the consumer shall be provided with the following information:
...
(b) the main characteristics of the goods or services;
I already said they don't have to get into all the details, but there's definitely a minimum. But let's not get too caught up in legal debates... it'll only get this thread closed.