The touchscreen and LCD panel are identical. Which means the aspect ratios are the same, pixel counts, etc.
The VGA PCB is very different. The 619 PCB is much smaller, seems to use the same or similar ICs. In all, it makes it cheaper to manufacture. My guess is the 619 will be phased out sooner or later.
Noted internal differences as follows:
619: The USB touchscreen circuit board is separate
629: The USB touchscreen is built into the main PCB
619: Main VGA connection via short pigtail
629: Big on-board connector for all the connections
http://www.lilliput.cn/619.htm
http://www.lilliput.cn/629.htm