Why does text-align center text and images?

CSS:
#SupplierContainer {
width: 100%;
margin: 0 auto;
background-color: Blue;
}
#SupplierContainerContentHolder {
background-color: Yellow;
text-align: center;
}
HTML:
<div id="SupplierContainer">
<div id="SupplierContainerContentHolder">
<img src="~/Shared/Suppliers/Default" alt="Suppliers: [name removed]." />
<br />
<p>View a complete list of our Suppliers.</p>
</div>
</div>
From W3,
Since
<img>is an inline-block element, this property applies to<img>as well.Have a look at the <img> tag, where it is stated :