Is it necessary to have <tbody> in every table?

Is it necessary to have <tbody> in every table? According to Standards.

Only if you define thead and tfoot. It is mostly used when the table has multiple bodies of content. If the data in the table is easily understood to be the tbody then you can safely omit it.

Quoting the HTML 4 spec: "The TBODY start tag is always required except when the table contains only one table body and no table head or foot sections. The TBODY end tag may always be safely omitted."

So, you must have a <tbody> tag if you have a <thead> or <tfoot>

See also: MDN

For the small fraction of your users still using IE7, you MUST add encapsulate your tr's in a tbody tag if you're building a table with the DOM methods!

This will work in all major browsers:

var table = document.createElement('table');
var tbody = document.createElement('tbody');
var tr = document.createElement('tr');
tbody.appendChild(tr);
table.appendChild(tbody);

This will NOT work in IE7:

var table = document.createElement('table');
var tr = document.createElement('tr');
table.appendChild(tr);

A quick blog post of mine on building tables:
http://blog.svidgen.com/2012/05/building-tables-in-ie7-with-javascript.html

^{It may be notable that I no longer make the effort to support IE7 on my own projects. The IE<=7 share is likely negligible for most sites at this point.}