Perhaps true - my problem with UMPCs right now is that wifi isn't very widely available yet, and although they can attach to cellular networks I believe the data rates are very high for tethering. I think WIMAX is being deployed soon in a few states though.
RIM seems to have a good grip on the mobile enterprise sector. I would be surprised to see RIM's (Black|Crack)berry crushed in that respect -- not because RIM offers the best product, rather because of a general resistance to change of that magnitude from an infrastructure point of view.
