Let me explain the reason why to you. First of all the SU-30 MKI India is in the process of buying from Russia are not 'junk.' They are some of the most potent aircraft in the world with considerable combat efficacy. They are maneuvrable, can carry highly effective ordnance, and have an amazing combat radius even without external tanks. Furthermore India has an agreement with Russia to coat some of them with a radar absorbment material coating to reduce their radar signature by around 70%.
And with a competent pilot and the full technology and weapons it can stand up to a lot of planes out there (apart from avant-garde jets like the F-22 Raptor which are a generation above the Su-30MKI).
Actually here ( http://www.flightjournal.com/articles/su27/su27.asp ) is a link to a site in Flight magazine where an American R-Admiral was saying maybe the US navy should buy several SU-33s to replace the F/A-18E/F Superhornets until the JSF comes into being. I think the best thing is to copy and paste the link if it is not direct. The article was in Flight Magazine and was written by Adm. Paul Gillcrist and the ex-VP of Advanced Programs at Grumman (they made the F-14) Bob Kress. Essentially 'Americanizing' SU-33s to take over the role of the F-14 Tomcat that was cancelled in favor of the F/A-18 (and in essence it says the F-18 cannot fill the shoes of the F-14, but that the SU-33 can). Thus it is not junk.
And i know someone will post a photo of the crash yesterday of a SU-27 and claim it is a sign the jet is 'junk,' but all i have to say sh!# happens, especially when the safety buffers of foreign airshows are not as stringent as in the US (eg they let jets fly very low over crowds over there).
Now for the second reason why they would chose the Sukhoi over the F-16. Pakistan is the reason!
The US sold some F-16s to Pakistan some years ago (we refused to deliver some of them, but several had already been delivered some time before). The catch is that these Falcons were 'dumbed' down ...they were what is referred to as 'monkey-model' versions since they lack any modern technology, dampened avionics, archac targetting systems, and lousy weapon payloads. For example when it comes to weapons the Pakistani F-16s can only shoot infra-red Aim-9 SideWinders, with a range of only a few miles and no beyond visual range capability.
In comparison the Flankers (SU-30MKIs) being bought by India have modernized avionics and weapons that can shoot down Pakistani jets while they are still in Pakistani airspace! And Russia plans to sell to India jets that are actually quite enhanced unlike the Dummy version F-16s sold to Pakistan.
Now the question is this: If the US was going to sell India F-16s that had the same technological and combative capacity as the ones used by the USAF (or Israeli airforce for that matter) then India might have decided to pick up the F-16s. However chances are the US would not sell advanced technologies to just any country and thus India might not get what i refer to as 'real' F-16s but instead may receive silly jets that look like F-16s (for those who know Falcons they would get F-16As) that can only fire Side Winders!
Given that choice i would rather take a SU-30MKI that can fire weapons witht he ability to take out a target 70 miles away and is ranked as one of the premier air-superiority fighters by several Western agencies like Janes Defense Group.
Anyway have a look at that article written by the Admiral and see what i mean.
I would not call the SU-27/30/33/35 'junk' and i would not buy F-16s if they were the same as the ones sold to Pakistan. Now if we were talking about the ones sold to Israel, or the ones used by the USAF that would be a completely different story since those Falcons are killers! However comparing Indian SU-30 MKIs with PAKISTANI F-16As is ludicrous because if the two nations went to war the Indians SUs would probably destroy all the Pakistani Falcons before the F-16s even left Pakistani airspace. It would be a slaughter!