Yes some LD people are lazy towards their relationship. They may also be procrastinators and hate broccoli.
The varities of LD and HD people are as diverse as the variety of people you see in the general population. This board alone has shown that to be true.
But I don't believe that LD people in general are lazy, period. I think that many can get that way, due to their own selfish human nature (which we all possess) as well as the relational dynamic that is present that ALLOWS it to happen. That is, the HD person tolerating it for years on end and then wondering why their spouse doesn't do more.
I believe that just as many LD people are not lazy when it comes to relational issues and just relate in different ways, besides sex.
For me, a "relationship" can be defined in romantic and "couple" type terms...intimacy, sex, quality time spent together, love, etc. For my H, I suspect that his list would define it with more action-type words: doing things together, raising children, building a life and home.
Both of these things are necessary to a marriage so it is impossible to say that one is better than the other.
So my vote would be no, it is too oversimplified to say that all (or even most) LD people are lazy.