The difference is while I might lend my book to one or two friends your 'internet friend' is lending his copy to thousands of people. The other significant difference being that while my friend has my book I can't read it unlike your 'internet friend' who can still watch the origional DVD while thousands of other people can watch the copies simultaneously.
While yes in isolation you can say the two activities are the same the cumulative effect is entirely different and warrants a different response.
Given the massive massive difference between download and upload speeds, I'd very surprised is any one user has made something they have downloaded available to 1000s of people. Most people don't even get to a 1:1 ratio, so you have only shared snippets of the media across 1000s people, not 1000s of entire copies.
Piracy has lead me to make a lot of purchases I never would have (mainly tv box sets and some great movies).
When was the last time you saw any "artist" driving around in a 1990's Ford Fiesta. I fail to believe that piracy has an impact on the industry, in fact id go as far as to say that it actually boosts sales of GOOD content.
If I go to a restaurant and the food is unacceptable, I can return it. If I buy an item from a shop and it is unacceptable, I can return it. Media does not allow for this. If I pay £12 to go watch a film at the cinema, and it turns out to be terrible, tough, I still lost my money.
But at the end of the day it's their business they have the. Right to charge what they want and if you don't want to pay, they go bust and you won't be able to get hold of their goods.
But the above is happening right now anyway, hence them QQing about loss of revenue.
So what happens to film and game review sites? If a game is released and panned by everyone, that results in loss of revenue for the game company. Are they going to block all review sites?
My friends sees a film I was going to see, tells me it's crap and I pass on going to watch it. Loss of revenue! Should my friend be punished?
Hell, releasing special editions shortly after the release of media can harm the initial batch of sales. Should the company sue itself for causing it's own loss of revenue?