Well, a yes or no answer could be misleading.
Yes, there is a difference in circuitry. Is it significant? It depends. The bulk of the preamp circuitry is identical.
But... if you think about it... the Beta Series (like a Beta Lead) is powering both a power amp and a preamp from a common power supply.
With a preamp only (e.g. a PL-10), the power supply doesn't have to supply as much current. This means that the power supply to the preamp won't sag whenever the power amp draws heavier current at higher volumes - simply because the supplies are split. So, the separate power supplies allows the preamp to keep pushing the power amp even when the power amp is using all it can get from its supply.
This is why... with separate power supplies, the sound "sustains" more than it "sags". Vice versa with a common power supply.
Plus, the whole benefit of separating power and preamps is so that you aren't stuck with one or the other simply because it's built in.
Like... (ahem) if you had... say... a
working Alpha slave... for example... ... ...
