1. Again the whole ISO thing is a joke. How many iso's do you mount and how often. This seldomly used feature although great doesn't justify the headache of upgrading from 7. My NAS can also mount images.1) You asked for things that can't be done in 7. That is one. Linux has no place in this discussion.
2) You would need to purchase new hardware to hit 400MB/s. 10GigE switch, cables, and cards. It's not cheap. Windows 8 allows you to team existing gigabit NICs together on your existing gigabit network and combine their speed. Once again, you cannot do this in 7.
3) There are several. In particular, I'm fond of not having to learn another piece of software just to do the job. But at any rate, it's another thing that Win8 can do that 7 can't. As requested.
4) You cannot mount or use a ReFS pool or drive in any version of Windows prior to 8 (to the best of my knowledge). This includes XP. Furthermore, when attempting to move an XP "drive pool" to another system, you will often find it to be impossible unless the hardware is identical. Storage Spaces allows you to mix and match drives of different capacities, speed, and types. You can plug in the 2.1GB fiber channel drive you have laying around, and add it to the 4x300GB 15K SAS pool you've already created. I wouldn't recommend it, but you could. You could then take it all apart, stick it in a new server with 100% different hardware, plug all the drives in different ports, smack one with a hammer while chanting and ranting about how bad Windows 8 is, and still have all of your data available. Can't do THAT with XP.
2. The whole aggregation argument is silly. Unless you have a network of computers that are all running 8/2012 its a moot point.
If your running wireless its a moot point.
If you using Network Devices or SAN/NAS this again is a moot point.
3. Lots of people use free or paid alternatives. That are better and have better guest compatibility. Please enlighten me how you can run BSD, Solaris, Novell or SCO unix in Hyperv with out massive headaches?. You can even run things like nt 3.51 in it. (For fun). Just because you have a narrow usage of Virtualization that doesn't mean everyone else does.
4. I am not sure if this feature is an actual advantage or a disadvantage.
ReFS great so if your computer or a system crashes how are you going to access data if non 8/2012 machine is not available to you? No backwards compatibility either which MS excels at. This is not an advantage as far as I can see.
Storage spaces You have basically a cutting edge technology which has issues that have been acknowledged by MS to be problematic, its also a Software RAID solution. Lets ask around people what they think of MS software raid solution in previous iterations of Microsoft OS's. Again not backwards compatibility.
You also can't use previously purchased software to recover data.