I'd offer that this isn't true in my experience, but that what are required are skills - so a friend who was in intelligence reserves and was an electronics engineer during the week was very useful. It's about what you bring to the party - not just about direct equality of career in my experience.
Perhaps my comment was rather sweeping, and there are indeed cases where reservists bring unusual and relevant skills from their civilian professions. However, career synergy works the other way too - my former employer might well have taken a more benign view of my TA infantry service if it bought benefits to the company I flew for.
If I can get another job back in the UK I might look into the RAF Reserves. It might make it easier to negotiate weekends out of my schedule if I am doing something that is easier to justify to the employer.