Is it possible so that the download size is going to be smaller by including only the changed files…
It is unclear. Do you mean if installer is going to be smaller by including only changed files or do you mean if LO is going to be developed in small steps? The latter one is true, first is not.
Even the second point is not true in every context, as the upcoming v4.1 has fixes for over 1000 bugs 
like you though I don’t really understand the question. Presumably it is a reference to the type of patch / update method used by Microsoft as opposed to that used by Apple.
what I meant is that, for an update we only have to download the changed files.
Thanks for clarifying. I have provided an answer.
First off I know this is a very old Question, just felt like complaining.
It is quite an annoyance not having patches that the program downloads and installs, and instead having to as of 5.0.5 manually download the full updated program, and manually install it just like OOo. I guess the only positive is the lack of a new folder being created on my DESKTOP of the install files like OOo did every dang time I updated.
The issue of providing a partial/diff-type (a.k.a. incremental) update mechanism is evidently an old issue that the developers are well aware of and working on. The related bug is fdo#54242. A couple of user mailing list threads from Jan 2012 and Dec 2012 are indicative of some of the non-technical issues. The comment by Charles Schulz in the December thread IMO offers the most important piece of information:
… developers know it’s important but given the nature of our legacy code it requires a lot of efforts - or a lot of money.
This AskLO question is also related.