WRF model development is done in such a way that users can run the model independently before you start adding more complex options to ingest observations. There is even an "ideal" mode that new users can take advantage of to learn how the system works (not for simulating real Earth situations). In "real" mode, there are typically two types of simulations done: a forecast or a retrospective (historical) simulation. It's important to have real observations ingested into a retrospective simulation, since the intent is to model the event as best you can. However, this is not possible in forecast mode, since the observations do not yet exist. So, it is important to have default lookup tables that characterize your unknowns.
Regarding the values in the LANDUSE.tbl, there are many groups that use the monthly MODIS-derived values to ingest into their simulations that replace some of these values. A "summer" and "winter" lookup table is provided for users in WRF, but those defaults are not appropriate for the best retrospective weather simulations. Forecasting, on the other hand, can use old satellite data (MODIS land-surface data is several days if not weeks old by the time it is processed) but that has error just as a seasonal average would. The values in the LANDUSE.tbl (except surface roughness) will get overwritten with the VEGPARM.TBL values if you use Noah or the RUC Land Surface Model (LSM). Noah uses monthly values as far as I know. RUC might write values on its own... not really sure if it uses the VEGPARM.TBL or not. I'm sure there are experienced WRF modelers out there that can give you more detailed information, e.g. on the WRF modelers forum.