That's no more true.
Both the new Mac Pro (to be released in a few weeks) and the latest iMac from Apple offer PCIe SSDs. They look to be made by Samsung.
Thereâ€™s flash storage, and then thereâ€™s next-generation PCI Express flash storage. Weâ€™re talking storage thatâ€™s up to 2.5 times faster than the fastest SATA-based solid-state drive and up to 10 times faster than a 7200-rpm SATA hard drive. Most flash storage systems connect via SATA buses designed for slower spinning hard drives. But we designed the new Mac Pro around new PCI Express-based flash controller technology to deliver the fastest solid-state drives available standard in a desktop computer. So booting up, launching apps, even opening massive files happens in, well, a flash.
Samsung has long considered switching to PCIe and other interfaces.
I think GB/s speed is no more reserved for RAIDed drives. 2GB/s will soon become the new norm.
Samsung's PCI Express SSD XP941 Reivew (in Korean, supports AHCI)
Samsung's PCI Express SSD XS175 (supports both AHCI and NVMe)