tested on Windows XP 32 bit professional, Windows 7 64 bit professional
2.72 eb464ee http://download.blender.org/release/Blender2.72/blender-2.72-rc-windows32.exe
2.72 fe42ceb https://builder.blender.org/download/blender-2.72-fe42ceb-win32.zip
Short description of error
According to wiki and blender.exe --help
Option -o must have specified filename ("-o Set the render path and file name"). In Blender 2.71 9337574 and previous path specified without filename works fine. Render is saved just in specified directory. In Blender 2.71 d919218 and next Blenders this doesn't works. Blender just quits and don't produces any warnings. I expect that if option -o really must have specified filename - then Blender must prints warning when specified path is directory. Or just renders as previously.
Exact steps for others to reproduce the error
"c:\Program Files\Blender Foundation\Blender\blender.exe" -b c:\tmp\untitled.blend -o c:\tmp\ -f 1
What happens: Blender Quit - don't render.
a) just render frame and save to c:\tmp\0001.png
b) print warning/error
"c:\Program Files\Blender Foundation\Blender\blender.exe" -b c:\tmp\untitled.blend -o c:\tmp\#### -f 1