Instead, all browsers do the same stupid thing - try to load all 30 images at the same time, leaving you sitting there looking at 30 partial images.
On a higher bandwidth connection this would be faster. Loading small (say, 100KB) images on a connection where there is high ping to the server (say, I have a fiber optic connection, but the server is on the other side of the planet)in series is slower than loading them in parallel, because of the time spent waiting for the replies (setting up the tcp connection etc).
I also remember download accelerators that would split up a file in multiple parts and download them in parallel, this would usually make the download faster even if all pieces came from the same server. Also, iperf -P10 is usually faster than iperf -P1...
Of course, on a very slow connection, loading multiple images in parallel is worse because each session is competing with the others for bandwidth and the downloads may time out.