The 100 watter has more filtering and bigger iron.  This contributes to tighter and punchier bass, it also make the amp a little stiffer and less touch responsive...a la less warm and vintage-y.  There is also the "perception factor"... amps sound different to our ears at different volumes...turning ups up usually makes them sound bassier and fuller. 

Overall, I think the tonal differences (volume withstanding) are vanilla vs. french vanilla.  You can only tell a difference IF and only IF you had them side by side.

Don;t forget, you can always pull two power tubes and rebias to make the 2203 a 60-watt or so amp.  It won't be exactly like the 2204 because the voltages and filtering will be different.