Gill, if you had an MG Midget Car Birthday Card for sale and a MG Midget fanatic came on site and searched for MG Midget Car, would you be happy that your card was not available to them? Their search is open and they want anything connected with MG Midget Car, whether is art work, cards, hats... anything. But they would go away from eBid because nothing would be available for them to purchase, yet there could well be 100's of items of interest.
Likewise, a new browser on eBid, searches for new baby pushchair - so under what you propose it takes them straight to the category. Maybe they don't see anything suitable or competitive, so away they go. However if they had seen your new baby card - they may have signed up to eBid and purchased the item, so a potential lost sale and a lost new sign up. The item is relevant to their search and that is exactly the way to sell cards.
The amount of examples like this run into the many 1,000's - I know I would have lost 100's of sales if the search was not returning what people were looking for. The implications could be far reaching - a lot of items could be impossible to sell because of keyword/category crossover. This is why all search engines/facilities don't do this (or at least I don't know of one that does).