Why do we obsessively use the term - killer?

The Killer App, The iPod Killer, the YouTube Killer the list goes on and on.

What do we mean when we use this phrase? 

Hulu is being called a YouTube killer (TechNewsWorld, EGear, The UTube Blog, Silicon Alley Insider, Reuters)- so this should mean that they are in direct competition, right?

Joost is being called a YouTube killer - so again, one would assume that they are playing in the same market, right?

Now this is where I start to get frustrated.

  Joost and (presumably) Hulu are in the business of serving up copywrite protected professional made-for-tv television longer form content.  YouTube is America's Funniest Home videos; YouTube is by and large a UGC clip factory.  We don't go to YouTube to watch clips longer than 10 minutes in duration (and I believe YouTube places the maximum video length somewhere around there).  Other than music videos, Joost doesn't have much that is shorter than 10 minutes long!

YouTube is for leaning forward viewing, mouse in hand, actively watching.

Joost is about lean back viewing - and multitask picture-in-picture viewing when in windowed mode.

I would completely understand if we were putting Hulu in competition Joost, Veoh, potentially Babblegum, and maybe even Zattoo if it ever makes it stateside, but where does YouTube fit in?

Are we suggesting that the launch of Hulu will create a new depository of clips from television shows that YouTube won't be able to stream for intellectual property reasons?  While this would probably present the strongest case for direct competition between Hulu and YouTube, I would like to present two objections to this argument as well:

1. While Hulu has principle rights to stream content from their sponsors, fair use laws still apply. YouTube users will still upload pirated content and Fair Use laws will often justify YouTuve's streaming of these short clips.
2. From a marketing perspective, if Hulu wants to play in the world of clips, they should work WITH YouTube, not against YouTube. 
   
   • Hulu is the new kid of the block, YouTube has a gargantuan established audience.  Rather than removing content from YouTube, Hulu should both post and encourage users to post short clips - 45 seconds or shorter - of Hulu content on YouTube with a Hulu logo embeded in the corner and Hulu splash screen after all content.  If I were Hulu I would even work with YouTube to run advertising before and after their new little pop-up ad bar - containing a link to Hulu (this is advertising on the little bar  before and after the regular advertising, not pre roll or post roll).  Everybody would win.

Let's not call something a Killer unless it's in direct competition with the existing category leader OR it can easily obviate the need for an existent product or service.
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In other news, how is NBC going to handle digital paid content distribution now that they've broken ties with Apple? 

Is Hulu about to become iHulu with a direct to download sales component? 

And if they do bake in this offering - how will they enforce DRM against the largest media distribution/player portal (iTunes - iPod) without working together with iTunes on DRM?