Re: Yes, but
"They had a lower capacity than a 1.44Mb 3.5" disk (IIRC, 180K per side), "
The Amstrad PCW came out in 1985, two years before the 1.44MB 3.5" floppy. It was, however, contemporaneous with the 720KB 3.5" floppy disks. By 1987, when the 1.44MB 3.5" disks arrived, Amstrad had updated to double density, 360KB per side or 720KB per disk. A few years later, they switched to 3.5" disks on the PCW, probably because they had now became cheaper than the now obsolete 3" drives. Bearing in mind it was built to a price, I wonder if an 8-bit Z80 CPU could manage with an HD 3.5" 1.44MB floppy or if they simply didn't see the point in changing again. After all, the target market wasn't power users :-)
Sometimes people just don't remember (or weren't there to know) just how fast computers were evolving back then and the various routes hardware makers went down only to find they chose the wrong route. There was no real reason those 3" drives could not have been double sided, they just got beat out by the Matsushita 3.5" format. It could have been one of the other competing formats that were also aiming to out compete and out perform the 5.25" floppies that had reigned supreme. At least we never standardised on the IBM 4" floppy!