Every program sold for computers is upgraded from time to time. This is not something peculiar to EQ. You can continue to use the old software if you want, but the new version will offer more options. Many people are still using EQ5 without upgrading to EQ6, and EQ6 has been out for some time. Upgrades come out when significant changes have been made to a product, not just for every little change. I was not quilting before EQ6 was available, but I understand that it is a major improvement over EQ5 in user friendliness and functionality.
Usually when an operating system is upgraded, it will continue to run software meant for the old OS, but after several upgrades it will not reach back that far.
With EQ6, you can download the latest fabric from many of the manufacturers. The downloads are free, so if you are using a new fabric line you have a good chance of finding it online without having to scan in your own fabric. Just colors are not enough for me - I want fabrics - but I haven't found it necessary to start scanning in my own since so many different fabrics are available already.
EQ helps you design your own quilt and block patterns. Even if you start with a known quilt pattern, you can explore different borders or sashing, or see what the quilt would look like with a different color scheme. You can easily change the size of a block with EQ. If you're doing a log cabin, for instance, it is easy to set the blocks into the quilt and then turn them every which way to decide on a layout. EQ will print out a pattern for paper piecing, templates for cutting patches, directions for rotary cutting, yardage estimates.
If all you want is to find patterns and make them, you do not need EQ. If you dislike using computers, you will not use EQ. However if you find yourself making changes in the pattern or designing your own quilts, EQ can make the process faster, more accurate, and more enjoyable. You will be more productive using EQ. (Unless, that is, you spend all your time designing quilts in EQ and no time sewing. Some people actually do that...)
I think that upgrades generally cost about half the cost of the new product, so roughly $75 instead of $150. If you buy EQ6 as an upgrade to EQ5, you must have EQ5 installed in order to install EQ6. After installation, you will have both programs on your computer. You can open the EQ5 projects with EQ6, but not vice versa. You may want to uninstall EQ5, but you don't have to. You do need to retain the EQ5 product in case you need to install your EQ6 again.
This site will give you a lot more information about what's in EQ6.
http://www.electricquilt.com/Shop/EQ6/EQ6.asp