Ilford's recommendations are always for the production of the highest quality archival images, made on a consistent basis. So if that's what you want, then follow Ilford's recommendations, if not, then you can ignore the recommendations.
Now the life of paper developer used in trays and used in drums is going to be different, due to air exposure. Developer that has sat all day in a tray has seen a lot of oxygen, where as developer that has been in a bottle and poured into a drum several times has seen considerably less oxygen, so will probably last much longer. Plus if your drum uses only a small portion of the total solution (which most do), then when it's poured back in the bottle it mixes with the remaining solution, becoming partly replenished. Trays tend to use large volumes of solution, so this does not occur. Usually for B&W paper developers they assume trays.