Excellent question. This is of course one example of the importance of every phrase and word that Fitzgerald has carefully selected in this novel. Note what we are told about the history of the mansion that Gatsby purchases in Chapter Five:
A brewer had built it early in the "period" craze a decade before, and there was a story that he'd agreed to pay five years' taxes on all the neighbouring cottages if the owners would have their roofs thatched with straw. Perhaps their refusal took the heart out of his plan to Found a Family--he went into an immediate decline. His children sold his house with the black wreath still on the door. Americans, while occasionallly willing to be serfs, have always been obstinate about being peasantry.
It is clear that some crucial parallels exist between the former and present owner. Both have emerged from the obscurity of the lower classes to rise up above their roots, and have built or purchased this mansion to make a very definite comment about their prestige, wealth and status now. The brewer's crazy scheme to get other houses to put thatch on their roofs demonstrates both his excessive wealth and his own sense of superiority as he tried to get others to do what he wanted. This of course finds its parallel in the childlike belief that Gatsby has that he can re-make the world according to his own personal desire, with barriers such as Daisy's marriage to Tom and her daughter proving to be nothing to his dominant will.