(I'm the datacenter manager at imgix, and I wrote the article)
I completely agree with your concerns, and I'm constantly evaluating our business for operational risks and inefficiencies. There's a lot of stuff that I can't share in public about this, but what I can say is that the math works out (for now): OS X graphics processing is worth the downsides. It may not always be the case, and we're built in a flexible way where we can make a change when it makes sense to do so.
How different is it? Aren't they dependent on OpenGL and Nvidia/AMD GPUs/Drivers themselves? Wouldn't it make better sense/efficient to invest in becoming platform agnostic and optimize this.
I only say so cause it seems like Imgix could massively benefit from such a move and maybe look into other solutions which you currently can't consider (Custom ARM silicon - PowerVR-based servers, Professional AMD/Nvidia GPUs, etc)
Without going into too much detail about our stack, there's quite a bit more to Core Image than OpenGL+graphics card driver.
Those are important components, and we're not talking about splitting the atom here, but Apple has had a number of smart people working on graphics technologies for a long time now. imgix also has a bunch of smart people working on this, but for a much shorter period of time.
I completely agree with your concerns, and I'm constantly evaluating our business for operational risks and inefficiencies. There's a lot of stuff that I can't share in public about this, but what I can say is that the math works out (for now): OS X graphics processing is worth the downsides. It may not always be the case, and we're built in a flexible way where we can make a change when it makes sense to do so.