The above are as well but they also deal a lot with raw engineering problems which lend well to being shared and communicated with others.
Apple is more in line with Microsoft (what with the operating systems and all) than your other examples. Apple should be duly faulted for their closed nature ways in this context.
Steve Jobs: "Apple views itself as a software company"
The Apple Store sure sells a lot of hardware - proprietary hardware, no less - for a "software" company.
How much software in the App Store is written by Apple?
A "software" company that writes software that only runs on its own proprietary, tamper-resistant hardware?
A "software" company that sues competitors not on software copyright infringement but on hardware design patent infringement?
Apple might view itself as a software company, but I am quite certain they are still a hardware company. If they were to only sell software and stop selling hardware, then I believe their business would fail.
They just don't have generic "research" divisions like the other companies. This is one (of many) result of Steve Jobs return - anything that wasn't product focused got canned.
Note, there is no Research-Publications at Apple. They do their research secretly and silently.