It's not theft. It's worse. Theft of something like a television means just that physical physical is stolen. It's the cost of doing business.
Over time, if piracy is not stopped, users will get the idea that your software is free and will be unwilling to pay for it in the future. This has the potential to destroy the profits for your entire product. Big companies like Microsoft and Adobe can handle this, but it's devastating to a smaller company.
Companies also lose money through support calls from people that haven't purchased the product (this happens more than you think).
Think about the newspaper industry: It's dying because you can get news stories anywhere, for free. Why would it be any different for the software industry?
Torrentfreak is a pro-piracy site. They want to change the word "theft" to something positive so piracy is accepted as a positive thing. It's not positive.
Piracy is the equivalent of a big company farming their work out to China: they don't want to pay the big prices here (software that's expensive) or worry about restrictions (drm/copy protection), so they go somewhere else where it's cheaper (piracy sites/bittorrent).