1. if the "arched top" term was used as opposed to a flat top like the SRX have, then yes, all SRs have very slightly arched top bodies. BUT if you were reffering to a true arched body (front to back - like a W Thumb, for ex), then no, the SRs don't have arched bodies since the back is flat.
I think the term arched top means the top is arched, just as it says. The top of my SR505 is arched and the back is not flat though it does have a flat area that straddles the neck attachment area and then arcs down to the electronics bay cover behind the knobs. Much of the back is curved and roughly symmetrically so with the front. Ibanez says this about the SRA:
SRA SERIES BASICS
Arched tops with flat back bodies
While their description of the SRT (I don't see an SRX in their current lineup) sounds like what you call an arched body:
SRT SERIES BASICS
Ergonomic arched top with scooped back body
Ibanez does not describe the SR body shape, possibly because it varies with model. The SR250's appear to have slab bodies. I think the SR300 body is similar to the SR500 but there could be differences in detail.
I like what they did to the SR305 for 2012: better pickups, better preamp, and better bridge. Unfortunately I dislike one thing they did to it, dropping the starlight blue color, and I like the SR505 preamp better otherwise I'd have gotten an SR305. I don't think you can go wrong with one. I'd have preferred a painted body bass actually.
Ken