[Mp4-tech] H.264: about Boundary Strength in Deblocking Filter

[AngelZhang innosis.com.cn]

hi,experts
In the H.264 standard,value of boundary strength is calculate according to
judgement of different macroblocks, such as mb_type and the prediction mode
etc. but I am confused why value of boundary strengh of IntraMb (here 4 or
3) are larger than that of InterMb(2,1,or0). is it mean that the filter
strength of IntraMb is stronger than InterMb? why?
and another question is that whether deblock filter is only used for P
frame and I frame don't need deblock filter.
thanks in advance.
best regards
angel