Unfortunately there are many points in a window where a leak can occur. In older houses with timber or steel windows, the most likely cause is cracked or missing window glazing putty. The putty will dry out with age, crack or crumble away,resulting in a moisture entry point past the glass and inside the window. Newer timber windows may have sealant or caulking applied between the glass, timber frame and the timber battens, the glass can just require re-sealing to rectify the leak.
Aluminium windows in modern houses have vinyl seals between the glass and the aluminium frame, that can shrink over time, perish or just crack. The bottom sill aluminium track is designed with weep holes for drainage, but if the sills are full of dirt, fluff or debris has blocked the weep holes, water can leak into the house. This is quite common, look at your windows and you will see how much material collects in the bottom track.
Water can enter through the side of the window frame where it joins the brickwork, often with a movement joint in the brickwork or under the window frame, due to movement of the house structure increasing the gaps.
The weather systems that Australia face have changed recently and higher rainfall and strong winds combined are definitely creating greater leaking problems around a house.
I recently have seen many newer houses built in the last 10 years with water damaged window linings. The window linings are constructed out of MDF (Medium Duty Fibreboard) and are very easily damaged by water ingress, resulting in swelling and delamination. Older houses built around the 1970's to 1980's had Meranti window linings which can also be damaged by water ingress and then rot. The house windows built around the 1960's and prior were constructed with Western Red Cedar that was very good at withstanding moisture damage if painted, however after many years of neglect will also rot between the sill and stile or mullions
So all windows can and probably will leak, depending on the maintenance done to them over the life of the house or due to the prevailing wind and rain direction. The amount of protection from eaves and roof overhang also assist the windows from paint degradation as well as protect the window from rain.
Bay windows are very susceptible to water ingress problems, however until a heavy rain this may not be noticed.
If your house has leaking windows, soak it up the water with a towel, take photos of the location of the leak and have a glazier quote repair work. It's easier to fix a leak than replace a window or the damage caused by a leaking window.