Why when I do a search and there are only three relevent results (other than spam) does google have a link saying "Try your search again on Google Book Search" and then I click and it says there are no results....ok...so thanks for asking me to try...that was useless.
But wait...I tried another search and then there was another link that said: Try your search again on Google Book Search" and I clicked on it and suddenly there was something but it was "RESTRICTED" content....so it is a book search that is too hot to handle? I dunno but it seems like a useless click either way...both times I took a chance and both time I got a useless answer...thanks goofle!
I really don't think Google is so much interested in whether the book search is succesful or not, the real prize for google is the information gained for their AI from scanning all those books! - they really don't trust the information published on web compared to print where editors, publishers quantify, compare and cross check everything.
Well, they want to promote the book search feature, but if they wanted to only show the link when they know in advance that results are available, they would have to run a simultaneous search on book search prior to actually displaying the link to see if there was results available. That would require additional computational power, because it would basically be performing 2 searches.
One option for them might be to display that link for each phrase/keyword and then cache the result of the first search in boolean form (1=results available / 0=no results). If 1, they could show the link, otherwise they would know that it's not worth displaying the link since there are no results. I don't think they do that though.
Anyway, I've noticed those kinds of usability mistakes on various websites and search engines. In the case of Google & search engines, it's probably just an inability to dedicate the resources. In the case of other websites, it's most likely just poor design & usability.