So, is it accurate to say Ur is less compressed? If so, is this where the sonic difference is? Or maybe a part of it?
Accurate to say that? No. Guitar players use the term "compressed" incorrectly. Compression refers to reduction of dynamic range. Guitar players will often say something sounds "compressed" if it is lacking highs and/or lows.
UltraRes is simply more accurate. It uses a proprietary technique to achieve 170 ms of IR resolution with no added latency or CPU usage. Whether or not this accuracy is audible or desirable is up to you. Personally I find it audible and desirable.