im not a guru but I'll try to answer your question.
1. Do you know what is their driver for moving you to EAD if they are keeping your H1 valid? I can't imagine there being a real valid reason one way or another.
2. By the letter of the law, I believe switching from H1 to EAD means you are "abandoning" your H status. I don't know how the mechanics work here. I suppose if the company does not inform the USCIS, then your H status still technically remains but is illegal by the letter of the law.
Its not the end of the world if you go on EAD and if you don't have other constraints (dependents on the way, etc.), its no problem. Remember to carry your EAD card when you travel overseas though. That's your only ticket in.