Why do some pianos have the bass bridge connected to the long bridge?

[Calin Tantareanu]

Hello!

Why do some pianos have the bass bridge connected to the long bridge?
I've heard this also called a "ring bridge".
It's interesting to note that it became more popular in recent times, 
because several new concert grand pianos use it, such as the new Bechstein 
D280, B210 and the new Mason & Hamlin CC.
Other pianos that use it, as far as I know: Steinway D and B (perhaps C 
too), Yamaha CFIIIS. I've looked in a recent Yamaha catalogue and none of 
their other(smaller) models have the bridges connected. For the other 
manufacturers mentioned, I am also pretty sure that their other grand piano 
models don't have connected bridges.
So I'm wondering why this connection is used and why only in large pianos?

Regards,

 Calin Tantareanu
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