Since Avastar was released in 2012 we have offered Avastar with a Pay once, get free updates forever policy. This means that regardless when you purchased, and regardless how much effort we put into the development of our Tool:
If you purchased before december-2014 then you will never have to pay anything for new updates of the software.

We promised to provide free updates forever, and this remains valid for all who have purchased Avastar in the past! So don’t panic, you old Avastar users will receive free updates until eternity, at least as long as we live and as long as the internet exists.

But we can no longer promise this same free update offer to new purchasers. Since 5-dec-2014 we only give away one year of free update and support to new purchases. New purchasers will get an annual renewal offer instead. If a new purchaser declines the annual renewal offer, then nothing serious will happen. You can keep working with the product as long as you like, you just no longer get updates.

Remind: If you have already purchased Avastar at any time over the past 3 years,
then you get all future updates for free

Note: You can express your goodwill and switch to the new Avastar license at any time. You can do this by just buying Avastar again and thus release us from the infinite update for free guarantee. This would help us to keep the product support in a healthy state.

Excerpt from the new Terms of Agreement (README.txt):

Limited Downloads & Updates

With your purchase you are eligible to download this product.
The downloaded software can be installed on recent versions of Blender
and it will run without any time limitations (it runs forever).

With your purchase you also get one year free update and support.
For more detailed information please read:

We will offer you an annual renewal of your support for a discount
of 50% of the up to date product price. If you reject the offer
then nothing will happen, you may continue using the product as
long as you like. You only won't get new updates any longer and
we won't be able to offer you free support in that case.
Once again: This affects only new purchasers. If you have Purchased Avastar in the past, you will continue to receive free updates as they appear.