Income Support on grounds on incapacity

This is probably really simple and I’m missing something obvious but I cannot understand this one:
56 year old claimed IB 5 years ago and was only awarded NI credits.  This continued until his wife passed away and he then claimed BA for one year.  When this stopped he claimed ESA (all this time he has been in receipt of LRCC and HRMC of DLA).
He then failed the WCA and appealed this decision claiming ESA during the appeal process.  He lost the Tribunal and then made an application to the JC for as he puts it whatever he was entitled to.
JC+ then awarded him IS as incapable for work with the disability premium with effect Aug 2010.  When he queried it at his local JC+ they said it must be because of his HRMC.

I cannot understand why he is on IS instead of JSA.  Of course IS is working out better for him because he doesnt have to sign on etc.  He is quite ill but unfortunately he does struggle to get 15 points on the descriptors.

I want to call the JC and query why he is on IS but would like to check possible reasons first just in case.

Thanks for your help.

My thoughts:

Regulation 2(3)a of the Income Support (Prescribed Categories of Person) Regulations 2009 provides that where the SoS has determined that a person has incapacity for work before 30th December 2009 (appointed day) they remain a person able to claim income support.

However I’m not sure how this interacts with reg 2(2)a which refers to someone being entitled to income support immediately before the appointed day. It isn’t clear to me whether reg 2(3) is defining “entitled to an award of income support on the basis of a relevant provision” or adding additional conditions of entitlement to the usual conditions i.e. income below applicable amount etc. Therefore don’t know whether they are suggesting a person must have been actually entitled to payments of income support before the date or whether they just had to fit into the categories of people in reg 2(3).

Anybody else have any ideas?

Edit: Actually the more I think about it I don’t think this would apply to a new claim for IS…

Edit 2: reg 2 ESA (Transitional Provisions) Regs only refers to no new claims for IS for periods of incapacity that begin after October 2008. In this case his period of incapacity began before so he may be ok.