Speed control is unpredictable at best, but the situation is not improved by many pilots flying their own speeds, often without telling ATC.
That may be so....but a pilot initiated reduction is normally because there is a lack of,or breakdown of SA, on the part of the controller so the pilot errs on the side of caution to prevent a GA. This is the exact scenario I described a few posts back - it was obvious to us that "maintain 180 knots" whilst approx 2.5-3D behind the preceding at 6 miles from touchdown was not going to work. Even with our proactive slowing and then instruction to reduce to minimum on handover to tower only just worked out with clearance to land at 100'.
All totally avoidable with some less "sporty" vectoring and a bit of coordination between APP/TWR. The question is why Approach control so variable at BCN? At most other major European hubs it is consistent, logical and (mostly) works.