Ok.. not knowing about your environment is hard to tell,
but after reading Doman's comment.. makes sense if you are using
a vm... other than that.. I've found that detecting ssd seems to be
something that you can achieve for sure only by getting the hd model
and looking for it using some kind of service.

If your concern is HDD performance, you can query "Win32_PerfRawData_PerfDisk_LogicalDisk"
I included it on the sample, and called the object "hdperftest" ( it's commented ) or simply do:

oHDPerformance=wmiquery('Win32_PerfRawData_PerfDisk_LogicalDisk')

to get ( attached image ) performance test for all your logical disks.

( tests can take time 5-10 secs depending of your system ; no message will be shown while wmi query runs )

Marco