Alors peut-être que la loi a encore changé parce que j'ai lu ça ici
Non-immigrant visa (90 days, renewable to 1 year) -- if you plan to do business here, or reside with a spouse, or retire. This requires documentation of your intent, usually a letter from your employer or your spouse's employer, or a marriage certificate with your Thai spouse.
Type B: If you are coming to
Thailand for business, then you apply for a
Nonimmigrant B (Business) Visa. This 90 day visa can be
extended for up to 1 year (and again for the next year) if you subsequently get a work permit and can show you've been paid the minimum monthly salary (50, 000 baht for nationals of most Western countries, less for others, details below).
source :
www.thailandguru.com/visa-to-thailand.html
... et il est dit que pour avoir l'extension d'un an il faut avoir obtenu le work permit