Brendan,
The difference between Solaris and Linux is mainly scalability. Linux scales well on clusters such as SGI UV3000 scale-out servers, or top500 supercomputers. These scale-out clusters serve one scientist starting HPC number crunching workloads 24-48h. Scale-out workloads are easy to parallelize doing a calculation on the same set of grid points, over and over again. All this fits into a cpu cache and can run on each separate compute node. All SGI UV2000/UV3000 use cases are HPC number crunching, analytics, etc.

OTOH, enterprise business workloads (SAP, OLTP databases, etc) typically serve thousands of users simultaneously. They do pay roll, accounting, etc etc. Such workloads can not be cached in the cpu cache, so you need to go out to RAM all the time. RAM is typically 100ns, which corresponds to 10 MHz cpu. Do you remember 10 MHz cpus? This means business workloads have huge scalability problems because you need to place all cpus on the same bus, in one single large scale-up server. If you try to run business workloads on a scale-out server, performance will drop drastically as data is shuffled among nodes on a network, instead on a fast bus.

Thus, business workloads use one single large scale-up servers, with max 16 or 32-sockets. This domain belongs to Unix/RISC and Mainframes. HPC number crunching use large clusters such as SGI UV3000 which has 10.000s of cores.

The largest Linux scale-up server is the new HP Kraken. It is a redesigned old Integrity Unix server with 64-sockets. The x86 version of the Integrity maxes out at 16-sockets only. Other than that, the largest x86 server is vanilla 8-socket servers by IBM, HP, Oracle, etc.

Linux devs only have access to 1-2 socket PCs so Linux can not be optimized nor tested on large 8-16 socket servers. Which Linux dev have access to anything larger than 4-sockets? No one. Linus Torvalds? No, he does not work on scalability on 16-socket servers. There is no Linux dev working on scalability on 16-socket servers. Why? Because, until last year, 16-socket x86 servers hardly even existed! Google this if you want, try to find a 16-socket x86 server other than the brand new HP Kraken and SGI UV300H. OTOH, Unix/RISC and Mainframes have scaled to 64 sockets for decades.

Look at the SAP benchmarks. The top scores all belong to 32-socket UNIX/RISC doing large SAP workloads. Linux on x86 has the bottom part, doing small SAP workloads. The HP Kraken has bad SAP scores, considering it has 16-sockets. It is almost the same as the 8-socket x86 SAP scores. Bad scalability.

Thus, if you want to run workloads larger than 2-4 sockets, you need to go to Unix/RISC. Linux maxes out at 2-4 sockets or so. The new Oracle Exadata server sporting SPARC T7 (same as the M7 cpu) runs Linux and it maxes out at 2-sockets. If you want 16-socket workloads, you must go to Solaris and SPARC. All large business servers, use Unix or Mainframes. No Linux nowhere.

Linux = small business workloads. Solaris = large business workloads. And the big money is in large business servers. If Oracle kills off Solaris, then Oracle is stuck at 2-4 sockets (small revenue). Only Solaris can drive large business servers (big revenue).

It does not make sense to kill of Solaris, because then Oracle can not offer (expensive) large business servers. Then Oracle will be stuck at small cheap business servers with Linux and Windows.

Regarding Linux vs Solaris code quality:
https://en.wikipedia.org/wiki/Criticism_of_Linux#Kernel_code...