it happens, and the legalities really vary from company to company. a few years ago there was the "startup logo generator" or something like that here on HN it got so bad.
also, let's say I work for Staples in customer support. Me and my 3 buddies use Flock to communicate at work using Flock, and send files back and forth...now "Staples uses Flock."
Yes, and? When you build a product hoping for bottom-up user adoption (as opposed to getting the CtO to make a company wide mandate) then its totally fair to do this. Half the hosting companies on earth have Disney and NewsCorp and Nike and Starbucks logos on their client pages because an employee used his work email to buy a $5 shared hosting account for his mom's blog.
A lot of Show HN apps/websites using big companies logo, not sure why it is legal to do so, when I believe all is for marketing.
And I hope they will response to your comment.