I'm fascinated by this very popular concept of long distance relationships both as they take place in real life and online. I'm a professional counselor who specializes in evidence-based relationship counseling, and I've not seen any strong research that talks about what makes for a solid long distance-based connection.
I know that the emotional and sexual affair rate for married couples who live together is around 80% (50% of men and 30% of married woman have sexual affairs). The rate may be greater for emotional affairs or flirting as this is where the majority of transgressions start (at work and online in most cases), mainly due to a lack of awareness of the high risk level.
I would imagine that the same core principals that sustain a stable, healthy, long-term face to face relationship are also necessary in a long term distance relationship. These include:
1) Realistic Expectations about long term relationships
2) Solid Relationship maintenance skills that have been learned and practiced;
3) Protective relationship boundaries (strategies against flirting or emotional affairs) and very strong
I would assume that foundational relationship needs would be primarily emotional and social in a long distance relationship and would be met via telephone and electronic communication. For example, there would be little potential conflict around shared house work. Compensatory strategies would have to be negotiated around relationship needs that can't be met through physical presence to one and other (i.e. physical intimacy).