The waterproof rating is only an 8000 - what's the significant difference between an 8000 and 10,000 mm rating?

Tech Specs:

Material:

[membrane/laminate] Infinidry-8; [shell] polyester oxford; [lining] nylon taffeta, polyester tricot, polyester mesh 

Insulation:

polyfill (80g) 

Fabric Breathability Rating:

5000 g/m² 

Fabric Waterproof Rating:

8000 mm 

Hood:

yes, adjustable 

Length:

below hip 

Venting:

underarm mesh 

Powder Skirt:

yes 

Pockets:

2 front hand, 1 front chest, (internal) 1 media, 1 mesh goggle, 1 sleeve flap-closure 

Seams:

critical seams taped 

Recommended Use:

snowboarding 

Manufacturer Warranty:

1 year