Yeah, but the character can often simply be an observer. I don't remember the character's names in any of Asimov's robot short stories.
Watson is an observer in
Sherlock Holmes stories too, but that misses the point. The main character is Holmes, not the viewpoint character of Watson. We can tell because the character exposition focuses on Holmes. It is Holmes who drives the action, who faces the challenges, whose decisions shape outcomes.
There's no question that
HAL,
Andrew Martin and
Wintermute are all characters. They have psychologies and social identities. Their physiologies just happen to be cybernetic. You can tell that they're characters because we develop sympathy and empathy for them.
Each is also a victim of its technological nature as well as being, in a sense, a customer of human technology, which supports my earlier point. It's not that the technology
is a character in SF (the black monolith in
2001 certainly isn't); it's that technology can sometimes be
realised as a character. But that shouldn't be too surprising: animals can be characters too, e.g. in
Jack London stories. We can imbue anything with 'characterness' just by giving it psyche and social identity.
In SF as with all other dramatic fiction the interplay of reader sympathy and empathy for major characters is key to shaping the story; if we had no sympathy for the characters or empathy for their motives the stories would fail.
Literarily it's a bit odd that Asimov writes cybernetic characters better than most of his human characters, say. But that's true of quite a few SF authors of the period, and less true nowadays. I think that it's more a peculiarity of authorship than a sign of good SF design. Clarke, by comparison, wrote great human characters at times (e.g. in
Citizen of the Galaxy), and Heinlein, Herbert and Niven say, are memorable for their characters.
Inevitably, character design in a short will be sketchier than in a novel -- there simply isn't the space to create depth and layering. But I can't think of a great short of any genre that has bad characters, or a short with bad characters that couldn't be improved by fixing 'em up.

More to the point, hard SF attracts a lot of rational, objective types who sometimes overlook the importance of characterisation in fiction.
All successful fiction -- even hard SF -- is an emotional journey. The emotions are embedded in your characters. My advice: if you don't want to write strong characters, write an essay.
