The early warning system notification arriving at phones gives data on where and how strong the quake is so by a quick glance at the phone anyone can ascertain whether they should duck and cover or stay put. You have about 15-20 seconds to shut off gas (if at home), duck and cover etc. once the early warning notification arrives. To randomly run into the streets as we saw in NY and DC with the earthquake there is the height of stupidity.
Well, if there is a massive quake in a developing country then it is better to get out of the building because the building is likely to collapse. Think of Haiti, which was a moderate quake by Japanese standards.
In Japan the risk is higher to go outside.