The systems are programmed for at least the "legal minimum connection time", which means that, if you accept the suggested itinerary, the airline has at least some duty to eventually get you to your destination even if you don't make the connection. Occasionally they are purposely kept short, such as the 30 min connection times in Guam for Micronesia destinations. When I first had one of those assigned to me, I figured there wasn't a chance. Somehow we managed to clear customs/immigration in Guam fast enough and they expidited us through security, calling out our flight and bumping us to the head of the line, so we caught our connecting flight with minutes to spare, and that sort of thing is planned and occurs daily because of the fixed number of people making the connections. With larger international airports like Hartsfield and Bush, there can potentially be many other arriving international flights all carrying passengers connecting to tens or hundreds of flights, with no way for the ticketing computers or the airport staff to try or even care to try to assure passengers make their connecting flights. When connecting through big international hubs, it's entirely on the passenger to get it right and erring on the side of longer connection times is the safest way to do it.Just because an airline will sell you an itinerary with a ridiculously short layover is no indication you actually have a decent chance of making it, even for domestic flights. The system doesn't appear to have any basic common sense programmed into it related to layovers, never mind actually being intelligent. You need to determine for yourself what kind of layover makes sense (as you're doing) and book accordingly.