There are several cases where eastbound vs. westbound flights have different levels of service based on the fact that the eastbound flights are shorter and have block times underneath a certain cut off.
For example, RDU-ORD has a meal westbound only. The eastbound flights have sub-two hour block times. The same is true with DEN-DFW and COS-DFW - meals westbound only.
ORD-LGA and ORD-BOS is another example. Eastbound gets continental breakfast and nothing between meal times. Westbound gets hot breakfast and snacks during non-meal times.