Not everyone can have more than 10million EC - i can not yet.
People who can have more might already have that card or not require it.
Some might want it but just can not afford it yet.
You get the EC amount increase either via the C-Store or by being a Subscriber.
And he's right - if you don't have that EC Cap Increase, don't sell anything that's going to get you more than 10 Million EC, because once you hit that limit, anything else you make is lost and you won't get it back.
It's cheap as hell in the C-Store. My advice is just get it and don't look back.