Yes, it's heavier than some full-sized cabs, but lighter than others. It's also really, really compact. Photographs on the web somehow don't capture how small it really is. That makes it easier to carry, despite the weight.
The 40 lbs. of weight doesn't come from having two EQ channels. Rather, it comes from using ceramic magnets in the 4x5" drivers, instead of lighter neodymium that most manufacturers are using (including PJB on many of their cabs, I believe). But that is also what gives the clear, powerful tone on the BG-400. It just sounds very good.
Having two channels lets you plug-in both a bass guitar and an acoustic upright, with ready-to-go EQ customized for each instrument. Easy switching between songs or sets. Note: there is a separate mute switch on each channel.
(PS: I don't play acoustic upright. Maybe one day.)
OK, that clears it up for me pretty good! But while it does appear to be darn good now, I still don't want a BG400 because of the weight but that's only because I'm old. >
~ And I don't really need a BG400 anyway for the bassing I do. But tone junkie that I am I'd sure like to play with one a few times just to hear it... I really wish some of the local music shops around me would stock some PJB on their stoopid shelves! ~I doubt there's any PJB stock in the entire State of NJ! ~
ain't gonna try it first!! 
) the Rumble does the job!