In the 60A/L/M the depressurization only occurs with the APU gen as the ONLY source of AC power. Any hydraulic issues under those circumstances are happening on the ground without rotors turning. With the higher electric load of a 60B/R the logic module might be different and provide depressurization with more than the APU gen online. If that's the case, your explanation makes perfect sense.
I've actually always wondered why the current limiters were an issue with the main Gens on because of what you're saying...the main issue is not to blow the APU load when it's the only thing running. You may be on to something with the additional electric load in the B/R as to why that's a concern. I'm sure a Nerd Twirler could explain.