people who have problems with something are always gonna be heared from more. you're not going to find someone here starting a thread titled "my microSD reader works just fine!" (atleast i hope not). but if something breaks, there will be posts about it.
i'm sure most microSD readers that were shipped with the R4 are just fine, no need to be alarmed. I'm getting a shipment of 5 R4s tommorow, i'll test every one of them just to see if this problem is really that widespread.