re: wouldn't these computers still need a hard drive?
No. The mechanical drive is replaced with a 32 GB (or larger) Flash drive. No moving parts, solid state memory.
re: hasn't Seagate said there will be no loss of speed with the encrypted drives?
Compared to a non-encrypted mechanical drive, possibly.
Compared to a Flash drive, no. From the link provided by may1sep2:
The 1.8in 32 Gbyte SanDisk SSD, which SanDisk announced in January, increases performance by as much as 23 percent and is three and a half times less likely to fail when compared with HDDs currently available for the Latitude line, Dell said.
That's quite a performance boost. There's no way a mechanical drive with spinning media and read/write heads can compare to the performance of a solid state drive. And the Flash drives have become cost competitive. Very cost competitive.