Games and toys certainly don't have to rob kids of their playing alone time. I believe games (the kind you purchase) and toys have little relevance to healthy child development. Play, however, figures prominently in healthy child development.
Play that is child-initiated, child-controlled, and open-ended allows and encourages children to process information and to make sense of their world. Any toys and games that help facilitate this mode of play are a plus. Child development professionals frequently express concern that kids don't spend enough time playing in mixed-age groups. Too much of a child's play time is spent in reactive play (video and computer games) as opposed to creative play. And not enough time is spent playing alone.
Psychologically, kids need and use playing alone as their means of taking stock of their thoughts and emotions. Being bored because adults aren't entertaining them is a common complaint among today's youngsters. Where is the incentive for kids to invent their own creative play if parents feel they must keep them entertained and busy all the time? Jump-starting kids creative play with some ideas can be helpful (for instance, playing treasure hunt outside just when it's starting to get dark). Let them use their imaginations.