But trust me having extra cores is a good thing...
If your innovative mindset is still stuck in the proverbial box, then sure, having extra cores is probably a good thing. But if you're an outside-the-box thinking company like Valve seeking an innovative entry to market, then not necessarily. We don't know what Valve's design requirements are and how each trade-off is weighted, so the point is moot.
I mean like come on, you seriously want a dual-core for a gaming box? Let them have a bit more computing room! This is not 2005 for god's sake
Every other closed console manufacturer on the market is doing more of the same: inject dedicated hardware with steroids (on DRM lockdown and ridiculous failure rates to boot) and hope that easily amused consumers are sufficiently distracted by pretty eye candy to actually care about why they're playing the game to begin with, viz. to have fun. Although I don't personally play video games, here's to hoping Valve promotes genuine user experience over another faux pas gimmick.
Even ARM is moving on to 2nd gen quad cores already so why not a quad-core?
To name a few, because...
1.) blatant "monkey see, monkey do" isn't exactly considered a golden virtue (outside of China, that is);
2.) max TDP is proportional to the number of cores, working against a dedicated small form-factor console;
3.) price point is proportional to the number of cores, making entry into a competitive, highly elastic and volatile market that much more difficult.
Considering a dual-core usually is relegated to the not so much of computational efficient per watt but efficient per dollar
What's to say efficiency per dollar isn't more important than computational efficiency per watt in a market with an expected low obsolescence life cycle? Did we not learn anything from Sony's initial PS3 release?