Question on Lisbon treaty

I found this Europa site that answers some questions on Lisbon. They also allow you to ask questions. Here's what I asked. I'll update when it's answered.

Hi,

in your Q&A section you say that the Lisbon treaty is not easier to read because

"Changes to the EU's Treaties have always come about through amendments to previous Treaties: this was true of the Single European Act, as well as the Treaties of Maastricht, Amsterdam and Nice. The Treaty of Lisbon uses the same technique. The Union's two main Treaties will be renamed the Treaty on European Union and the Treaty on the Functioning of the European Union. The two Treaties will have the same rank.

A consolidated version of the Treaty will be published on 15 April on the web and on 9 May on paper version."

but this was not true of the constitution. The Lisbon treaty is a modified version of the constitution - modified so that a referendum is no longer necessary in most countries.

So, is there actually a reason why Lisbon treaty could not have been written as a consolidated piece of text, replacing prior treaties.

Specifically, is there a significant legal difference in how countries must treat a treaty which replaces prior treaties and one which amends them?