In general, in the last few years Apple introduced to the PC market: ultrabooks, Thunderbolt, OpenCL, HiDPI laptop displays (and a working resolution-independece software layer), consumer-grade tiered storage (Fusion Drive), unibody computer designs, long-duty compact laptop batteries (1000 load-cycles compared to 300-400 of manufacturers like HP) and industry-best touchpads. As far as iMacs go - nobody else can build a machine so thin with such a good thermal solution that it is able to fit a top-of-the-line Intel quad core and a fastest mobile GPU currently available. Some Windows gaming laptops with high-end GPUs are actually thicker than the iMac - and the 27" model with everything inside weights only a few kilograms more than your average 24" display!
These are things which come to my mind spontaneously. Can you name me a single other PC manufacturer with more innovations over the past few years?
I am fully aware of the fact that Apple products are more expensive than other products in the market and that they limited in many ways. You can criticise Apple for many things - but technological progress is really the last one which comes to my mind.
I totally agree with you, they have been the only company who has consistently come up with new ideas and been trend setters for a long time. Just in the last few years though, they haven't really introduced anything and just been updating or modifying their current lineup. I guess the public in general has been spoiled by Apple with their constant introduction of interesting products over the years.