Muslims Are Commanded To Deal Fairly Equally With Their Wives, Why?

[Quran 33:51Shakir]  You may put off whom you please of them, and you may take to you whom you please, and whom you desire of those whom you had separated provisionally; no blame attaches to you; this is most proper, so that their eyes may be cool and they may not grieve, and that they should be pleased, all of them with what you give them, and Allah knows what is in your hearts; and Allah is Knowing, Forbearing.

Another translation:

You, [O Muhammad], may put aside whom you will of them or take to yourself whom you will. And any that you desire of those [wives] from whom you had [temporarily] separated - there is no blame upon you [in returning her]. That is more suitable that they should be content and not grieve and that they should be satisfied with what you have given them - all of them. And Allah knows what is in your hearts. And ever is Allah Knowing and Forbearing."
Quran 33:51

Here Muhammad was told he could put off or put aside any of his wives at will. Is this dealing fairly and equally with a muslim's,wife as recommended by this:

[Quran 4:3 Yusufali ] If ye fear that ye shall not be able to deal justly with the orphans, Marry women of your choice, Two or three or four; but if ye fear that ye shall not be able to deal justly (with them), then only one, or (a captive) that your right hands possess, that will be more suitable, to prevent you from doing injustice.

Why would God set a double standard for Muhammad and other muslims?