~ 법이다 : It is normal(or natural, right, proper, appropriate, ... ) that ~ ~ 법도 하다 : There is a possibility that ~ , It is likely that ~

I cannot tell the specific difference between them. I feel that they are similar but the former sounds stronger. 법이다 is shorter with more determined voice, and 법도 하다 includes more of uncertainty. As in, 하이힐을 신고 그렇게 달리면 (당연히) 다치는 법이다. If you run in those high heels, you will hurt yourself. 네가 그렇게 공을 들였으니, 그녀가 너와 데이트 해줄 법도 하다. All that you have done for her, she may go out on a date with you. I hope you can get a little more sense on this issue. 도움이 되었길 바라요~