Why are we not seeing more 10K drives? Other than the WD Raptors, I haven't seen 10K desktop drives in forever.
I would think it would be a better compromise, am I missing something?
There are two sides to traditional hard-disk performance: rotational-speed and areal-density. While both increase performance of the disk, they do so in different ways...
Rotational Speed, measured in RPMs, primarily affects random access/seek times -- allowing the disk heads to move to a new location more quickly. This is handy when there is heavy fragmentation (which should never be allowed to happen) or when the data files themselves have lots of non-consecutive data (like in databases). Higher rotational speed will increase transfer speeds... but not nearly so much as most folks think it will. The disk access patterns for most desktop users do take enough advantage of this to make the increased cost worthwhile.
Areal Density, measured in bits/m^2 or bits/in^2, primarily effects continuous transfer speed -- you get to read/write large files more quickly. This will help you more quickly transfer files on your network (though many/most disks can easily enough saturate gigabit ethernet, these days) or load large files into memory, such as the case for video games or other applications with large resource files. Areal density does not have much of an impact on random seek times, and so those numbers haven't seen much improvement over the years. Improving areal density is something drive manufacturers have a keen interest in, as it allows them to build disks with more storage capacity, thereby decreasing the number of platters necessary for a given amount of space, and therefore dropping prices.
Also, keep in mind that, to keep friction/heat/wear-and-tear down, 10k RPM drives tend to have fewer and smaller platters than 7,200 & 5,400 RPM drives; they are hamstringed for storage space. Consider that we now have 4 TB 7,200 RPM drives on the market, but the largest 10k RPM drive is only 1 TB. And the price is about the same.
Both sides of the coin effect performance, but in different ways. Given the amount of time that 10k RPM SATA drives have been on the market, I think it's safe to say that these will never catch on, and that their price will always remain high. 15k RPM desktop drives is nothing but a pipe dream.
SSDs, on the other hand, have ludicrous transfer speeds married to access times that make a 15k RPM drives look pathetic. Their only two caveats seem to be storage space (they still can't keep with traditional hard disks on that, but they're catching up) and reliability. Though flash memory is far from ideal, we can expect both density and reliability to increase over time, even as their transfer rates continue to compete with small RAID arrays.
SSDs already outpace 10k & 15k RPM hard disks in ever measurement of speed. Given time, they will likely catch up in storage capacity and bytes-per-dollar. And, by the looks of it, that point in time is rapidly approaching.