It does matter in so far products come and go and you don't want to accumulate knowledge on a product that's going to disappear from the market.

I worked with SGI IRIX from 1991-1996. The company has since gone bankrupt twice and IRIX has disappeared from the market. All the knowledge I accumulated on IRIX is worth nothing because it's no longer in demand. Practically noone still has IRIX machines in production.

In 1996, I switched to Linux. It had a vibrant community and you could feel it's growing rapidly. Turns out that knowledge is still valuable.

So it's really important for engineers to keep a close eye on the marketplace: If something's getting out of business or out of fashion, stop investing time in it. Instead, be on the lookout for stuff that's growing. In general, open source stuff has a longer lifetime because it can be forked if need be, wheras proprietary stuff is often problematic as companies change their mind on a whim. HP/WebOS is a recent example.