I note that some AK's seem to have these and some don't (WASR's).  There doesn't seem to be any negative consequences of not having them - most of the WASRs I have seen and shot seem to feed as reliably as the AK's that have them.  

Question:  Are these really necessary?  Do they have a positive effect on reliability?  Does the mag wobble I have noted in some WASR's matter?  

Any thoughts on this would be appreciated.

Regards.

Something is needed. I think the WASRs have little plates spotwelded in instead.

ETA:

I think - but am not sure - that current production military AKs from Romania are the same way. I know the RPKs are.

no their not necessary if ya got plates of steel welded inside (like a wasr), but they do look good!..IMHO

Saigas don't have the dimples either - do they?  Any opinions on if these matter?  

Quoted: Saigas don't have the dimples either - do they?  Any opinions on if these matter?

A few were imported with military overrun receivers that have the dimples/Y stamps/various military details; I haven't seen many. Most don't have dimples but seem to work ok.