I'm pretty sure the reason for it being done by experience earned and not by advances taken, is that the rules suggest that potentially a PC can spend his experience during an adventure. This is a story, and PC could potentially "learn" (story-wise, "reveal") a skill/talent during the course off the story. So, rather than have group rank fluctutate during the course of a session, every PC who has gained X amount of XP has the potential to be the rank and is treated as that rank.

As a hypothetical example (not necessarily WFRP specific), a PC (John) has 1xp unspent.  During a session the PCs run into a group of Dark Elves.  John's player decides to immediately spend his 1 XP for John to know how to speak Dark Elf. He then procedes to fill in backstory about how he came to know the language. 

Really, I don't see the problem with using XP earned.

You give a good point dvang.

I don't have a big problem that character rank is done by experience earned (I am still doing it like per raw). I have been sometimes anoyed when a player saves some of his experience points, and when he gets his 10th xp he automatically trains 3 skills to his second rank while stille being in the first career.

Ok, it is not a big deal, I agree, but is annoys me a bit because when you only have 10xp having 2 yellow dice in 3 skills, makes a big difference. Specially, I don't like it if it becomes the norm.

Cheers,

Yepes

Well, keep in mind that PCs are restricted in the number of each type of advance they can take. They get 1 free skill to train, and the X more depending on their career.

In order to get 3 skills with two yellow dice, they would need to:

a) have three skills trained once at creation

or

b) Have two skills trained once at creation and have a career that has a 3 for skills in their career advances chart (so they could spend 1 advance to train a skill once during their career, and then 3 more to get a second training in all 3 skills at 10XP).

In addition, they have saved up 3 XP, not buying anything, for 3 (or more, depending on how often you give XP) sessions. Otherwise, it costs an addiitonal XP per skill trained as it counts as a non-career advance.

Really, chances of more than one getting two training at 10XP should be slim.

If it really bugs you and is a problem for your group, simply make a simple house rule that restricts acquiring/training skills to one purchase per session (for example).