In a review of an entry level DSLR, I found this:
[this] is an excellent DSLR but make clear that a DSLR is no longer the only way to gain large sensor image quality at this price [around $500]
What are the alternatives the reviewer is alluding to? Would they still have interchangeable lens?
To be clear, I'm not after specific models, I'm just interested in understanding the kind of camera the reviewer had in mind.
Apart from DSLRs which have normally the largest sensors (full frame or APS-sized) there are some other types of cameras that have at least larger sensors than the typical compact.
For example there is the Micro-Four-Thirds-Standard (see http://en.wikipedia.org/wiki/Micro_Four_Thirds_system), which has a relative large sensor (18 mm × 13.5 mm), but I don't think there are cameras in the price range about $500. If I recall correctly these cameras are rather in the $1k-area.
The best compromise between sensor size and price below $500 would be a compact with a larger-than typical sensor like a Canon s95 or Olympus XZ-1.
APS-C sensors can be found in some mirrorless cameras in similar price range, such as Samsung NX100, Sony Nex-3 or Nex-5. They do have interchangeable lens.
Also, Sigma's compact camera DP2 with an APS-C sized Foveon sensor is in same price range. It has fixed 24mm f/2.8 lens.
Note that prices fluctuate in different regions at different times, and even if some of those cameras are now more expensive than a D3100 it might have been different in past and/or in different area.
To specifically answer your question "What are the alternatives the reviewer is alluding to?"
If you go to this page of the review, you will see that dpreview have compared the image quality with the following non-dslr cameras:
They are both available (in the UK) for less money than the d3100. Note that I haven't tried any of these cameras so I couldn't advise as to their individual strengths.
If you are not sure which of these styles you prefer, try and find some friends with similar cameras, or failing that, try in a local camera store.
The only way to get large sensor quality is with a large sensor! It's just plain physics, no amount of technology is going to get round that. I have no idea what the reviewer was on about (linking to the review for some context might help)!
Large sensors are about more than just light gathering and noise. They offer many advantages:
There are of course non-DSLR cameras with large sensors, starting with the smallish micro 4/3rds cameras like the olympus pen, to the slightly larger fixed lens Fuji x100, and Sony NEX system, to the full frame Leica M9 digital rangefinder. The quote was referring to these other options.
I don't think it is hidden. It is simply stating that several mirrorless cameras are in a similar image quality and price as the D3100. As the article says "both live view and video are quite simply done better by other cameras, particularly the D3100's mirrorless rivals."
The article is differentiating between a DSLR, which provides an optical, thru the lens path that uses a mirror that pops up when the shutter opens, and a mirrorless or EVIL (Electronic Viewfinder with Interchangeable Lens) camera, which has no mirror, or even optical thru the lens capability, instead viewing the sensor itself via an electronic viewfinder.
what it means is that something has a product to sell that's priced like a DSLR but isn't a DSLR, and is trying to convince people to look for his product rather than a DSLR who are susceptible to "new and improved" as the main reason to buy something different from the established standard.
