Exactly. To put my engineer hat on, there are basically 3 types of loads on any structure: tension/compression, bending, and torsion (twisting).

On a conventional 2-arm skid steer the arms are in bending and compression and lift is done by 2 small diameter cylinders. 

On a single arm skid steer with the arm off center from the load the arm is in bending, compression and torsion and lift is done by one large diameter cylinder. Torsion is best handled by a tubular shape beam so the arm is a larger box shape which also handles the compression and bending. A single arm is just a different design that  takes a bit more steel in places but the trade off is that it allows a side door that a two arm design does not and better visibility in many arm positions. To me the side door is a major benefit.

In both cases the bucket, etc is centered on the wheels or tracks.

JCB's single arm design has been around for many years now and is also sold by Volvo. If there were any problems due to a single vs double arm the single arm machines they would not be around. The  single arm just requires different engineering.