My reasoning; If you keep/insert hard altitudes out of London then you better do it at all other ports as well. I know some operators do it. My current airline has no procedure/culture doing so. We're two pilots that go through the routing and stop altitude during the briefing. Has worked well so far and doesn't seem to cause any altitude deviations. Lastly the the FMC will only stop you if climbing in VNAV which many aren't doing approaching a low level off.