I don't think that's the basic premise. elementary is not just a GTK theme, they have their own set of apps (for better or for worse) which follow their HIG, they are rewriting productivity apps to use the EDS backend throughout the system, they are trying to improve gesture support everywhere... It feels a lot like what made OS X so great about a decade ago.
Even the basic premise that what people like about Apple is adequately described by "attractive to look at" shows the error in thinking.