Lets face it....2-core machine with 8G of Ram is still good machine for coding, web and mobile development. My iOS applications compile and build in Xcode very fast. When writing web code...it is so basic that 2010 machine can do it without a sweat. When i run pixelmator (mind you, it is basic) it gives me no problem (HD4000 graphics).
My friend runs professional design company (basically...he uses adobe products like photoshop, indesign, etc...) all day long on his 2-core i5 with 16G of RAM and is doing just fine.
Sure 4 core is good, but don't make it out like 2 core is useless machine. It is still professional machine....just not for 3D rendering and huge vide editing and rendering.
My Macbook air 2012 with dual core i5 and 8G of RAM is still going strong and is very fast. No need to upgrade for at least 2 years. But that is based on my needs (mobile and web development with light photo editing).