80% sounds quite high but I wouldn't be surprised if the number is around there. Google are big enough to take risks and try things that don't work out. There are 95 official Google products in the Wikipedia 'discontinued products' listing - https://en.wikipedia.org/wiki/List_of_Google_products#Discon..., but that's not very accurate in that it doesn't mention things have failed but are limping along, and it includes things that were discontinued but live on in other products (eg Wave merged with Docs).

It's not entirely unreasonable to suggest Google have 20 successful products for their ~95 discontinued ones though.. which would work out as 80% 'failed'.