I have never encountered a limited SMS (pay monthly) plan here (England). I think they're listing 10,000 as an alternative to saying "unlimited", or networks here are hiding this 10,000 limit in their TOS?

I'm with Vodaphone and I pay £36 per month for: "Your Plan comes with 300 minutes, unlimited texts, 500MB mobile internet and 2GB BT Openzone Wi-Fi" and I can't find any limited plans or information on a supposed limit on "unlimited".

Edit: aha! Found it, on the far right they clarify that 10,000 = unlimited.