Most fans require to Line feeds both switched and permanent which you diagrams do not allow for. There are a number of ways these can be wired from double pole lighting switches to standard three pole isolators depending on the protection required. Some fans require a 3 amp fuse where the lighting supply is normally protected with 6 amp devices. And also often extra RCD protection has to be added. So although there may be systems which could be wired as you describe it is not the normal way.
Why do you ask?
Also note that in your third diagram you are feeding two spurs from one socket which is not permitted under the regs (does ROI use our regs? or Part P?)
( and where would you put the junction box so that it is accessible for inspection etc?)
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