Originally posted by Mistral75 The aperture is controlled and commanded by an electromagnet and not a mechanical device. It's cheaper, more precise and allows for continuous and smooth variation in the aperture, which is a highly desirable feature in video mode.
All Canon lenses have such a device since the first day of the EOS system and so do all recent Nikon lenses (the "E" series).
Having the K mount allowing for electromagnetic control of the aperture is also important because it abolishes a barrier for third-party lens makers (think: Sigma) to produce K-mount versions of their lenses.
Another advantage of building up a portfolio of lenses with light focusing group and electromagnetically controlled aperture such as the 55-300 PLM RE: the day you propose a mirrorless offering, your clients can use these lenses with no drawback whatsoever, either directly if your mirrorless camera uses the K mount (KAF4 actually) or with a very simple adapter (spacer + connectors) if you choose the way of a new mount with a shorter register.
In both cases, your brand new mirrorless offering can rely on a portfolio of lenses from day one.
Clever move from Ricoh Imaging, isn't it?