Solaris

There must be a reason but I wouldn't spend time to investigate the Total vs Physical values discrepancy. It is unrelated to your issue anyway.
You are confusing RAM and virtual memory in your statement: Allocation is done on virtual memory, not RAM. When a process is asking for 2 GB of memory, no RAM is involved. Only when that memory is written to or read from is does it need to be in RAM, and that won't be 2 GB but the memory pages accessed, not more.
Unlike Linux, AIX and others, Solaris doesn't overcommit memory so it is making sure all allocations are backed by either RAM or swap at allocation time.
On the opposite, Gnu/Linux doesn't do it so in case of memory shortage, is just killing otherwise healthy processes to free RAM which might not be what people expect from their OS.

I am experiencing the same issues on SPARC systems now. I have two M5000 with 32GB RAM in each and could "boot" more than 3-4 zones. Once 3 zones were running, the amount of available memory would drop to 2-4G and I could not start another zone.

I have increased the swap on one of the M5000's and am going to attempt to boot the other zone.

This thread is a good read. Thanks jlliagre for explaining the memory configurations and ZFS swap file changes.

Have you enabled rcapd - resource capping?

I tried to configure that before and fubar'd the global zone server and had to rebuild it.