Here you can find a nice brief info how to read the figures you are seeing.
Let's get (non)volatile
And a bit more elaborate 
http://mcuoneclipse.com/2013/04/14/text-data-and-bss-code-and-data-size-explained/
For the time being the problem with Web IDE is, that the relative numbers are still refering to the Particle Core which only had about 20KB of SRAM, but the Photon has got 128KB of which some is used for the system and leaves you about 60K to start with.
The figure you get from System.freeMemory() should give you a “good” idea how much you have free at least, but the number can change while your program is running due to dynamic RAM allocation (e.g. by use of String objects or explicit malloc() or such).