Integral Weld Neck Flange Design Per ASME VIII, Div 1, Appendix 2

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What are the engineering reasons behind the hub slope limitations given in ASME VIII, Div 1, Appendix 2 Fig. 2-4 Sketch 6 for integral flanges? Is it due to stress concentrations?

Also, is sketch 5 intended to be for an integrally cast flange, where as sketch 6 is for a welded flange? I am assuming this is the situation because no minimum weld distance from the flange is given in sketch 5. Apart from weld detail and the slope limitations sketch 5 and 6 look to be equivalent. Is there a reason not to put a slope on the sketch 5 designs?

Thanks.